Category:2D materials - Revision history

Liebetreu: Reverted edits by Liebetreu (talk) to last revision by Wolloch

2026-04-15T12:24:57Z

Reverted edits by Liebetreu (talk) to last revision by Wolloch

← Older revision		Revision as of 12:24, 15 April 2026
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	Although thin-film simulations often employ the same computational setup and slab model as surface calculations, their objective differs. In thin-film studies, the goal is to investigate the behavior and properties of the entire system — including both surfaces and the bulk-like interior region — rather than isolating the characteristics of a single surface.		Although thin-film simulations often employ the same computational setup and slab model as surface calculations, their objective differs. In thin-film studies, the goal is to investigate the behavior and properties of the entire system — including both surfaces and the bulk-like interior region — rather than isolating the characteristics of a single surface.
	====2D materials====		====2D materials====
	This class of materials comprises ultrathin films consisting of only a few atomic layers. Prototypical examples include graphene, which is one atomic layer thick, and molybdenum disulfide (MoS~~<sub>2</sub>~~), which consists of three atomic layers. Such materials can occur naturally as van der Waals–bonded layered crystals, but they can also be exfoliated and studied as mono-, bi-, or few-layer systems.		This class of materials comprises ultrathin films consisting of only a few atomic layers. Prototypical examples include graphene, which is one atomic layer thick, and molybdenum disulfide (MoS$_2$), which consists of three atomic layers. Such materials can occur naturally as van der Waals–bonded layered crystals, but they can also be exfoliated and studied as mono-, bi-, or few-layer systems.

	==Slab symmetry and stoichiometry==		==Slab symmetry and stoichiometry==
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	If a slab is non-symmetric, it is important to consider [[Electrostatic_corrections#Using_the_dipole_correction_for_slab_calculations\|dipole corrections]].		If a slab is non-symmetric, it is important to consider [[Electrostatic_corrections#Using_the_dipole_correction_for_slab_calculations\|dipole corrections]].
	The non-symmetric 111 NaCl slab (Fig. 2) is forming a dipole, with Cl~~<sup>~~-~~</sup>~~ and Na~~<sup>~~+~~</sup>~~ terminations on opposite sides of the slab. This leads to a potential gradient through the vacuum, which is not physical and leads to extra interaction between the slab replicas.		The non-symmetric 111 NaCl slab (Fig. 2) is forming a dipole, with $Cl^{-}$ and $Na^{+}$ terminations on opposite sides of the slab. This leads to a potential gradient through the vacuum, which is not physical and leads to extra interaction between the slab replicas.
	In general, this can be true for any non-symmetric slabs, not only for ionic crystals like NaCl. In those cases, dipole corrections should always be turned on and the size of the dipole checked in the {{FILE\|OUTCAR}} file. However, energy differences due to dipole interactions are usually smaller than energy differences due to a different [[exchange-correlation functional]]. They can also interfere with convergence during [[structure optimization\|relaxations]]. It is thus usually advisable to initially relax the system without dipole corrections and then turn on the corrections in a static follow-up calculation. If there is a resulting dipole, a follow-up relaxation can be performed using the {{FILE\|WAVECAR}} file from the static calculation as a starting point.		In general, this can be true for any non-symmetric slabs, not only for ionic crystals like NaCl. In those cases, dipole corrections should always be turned on and the size of the dipole checked in the {{FILE\|OUTCAR}} file. However, energy differences due to dipole interactions are usually smaller than energy differences due to a different [[exchange-correlation functional]]. They can also interfere with convergence during [[structure optimization\|relaxations]]. It is thus usually advisable to initially relax the system without dipole corrections and then turn on the corrections in a static follow-up calculation. If there is a resulting dipole, a follow-up relaxation can be performed using the {{FILE\|WAVECAR}} file from the static calculation as a starting point.

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	===Surface-energy calculations===		===Surface-energy calculations===
	The surface energy, ~~<math>~~\gamma~~</math>~~, is an important characteristic of any surface, determining its stability and influencing its adhesion properties, catalytic activity, and ability to form thin films and interfaces.		The surface energy, $\gamma$, is an important characteristic of any surface, determining its stability and influencing its adhesion properties, catalytic activity, and ability to form thin films and interfaces.

	For a symmetric and stoichiometric surface slab, the surface energy ~~<math>~~\gamma~~</math>~~ of the two equivalent surfaces is given by:		For a symmetric and stoichiometric surface slab, the surface energy $\gamma$ of the two equivalent surfaces is given by:
			\begin{equation}
	~~<math>~~
	\gamma = \frac{1}{2A}\left[E_\mathrm{slab} - N E_\mathrm{bulk}\right] \quad,		\gamma = \frac{1}{2A}\left[E_\mathrm{slab} - N E_\mathrm{bulk}\right] \quad,
	~~</math>~~		\end{equation}
			where $E_\mathrm{slab}$ is the total energy of the slab, $E_\mathrm{bulk}$ is the total energy of the bulk, and $N$ is the number of formula units in the slab relative to those in the bulk cell.
	where ~~<math>~~E_\mathrm{slab}~~</math>~~ is the total energy of the slab, ~~<math>~~E_\mathrm{bulk}~~</math>~~ is the total energy of the bulk, and ~~<math>~~N~~</math>~~ is the number of formula units in the slab relative to those in the bulk cell.

	~~A more general formula, that holds for non-stoichiometric and non-symmetric slabs for the surface energies <math>\gamma_1</math> and <math>\gamma_2</math> on both sides of the slab is~~

	~~<math>~~		A more general formula, that holds for non-stoichiometric and non-symmetric slabs for the surface energies $\gamma_1$ and $\gamma_2$ on both sides of the slab is
			\begin{equation}
	\gamma_1 = \frac{1}{A}\left[E_\mathrm{slab} - \sum_i N_i\mu_i(p, T)\right] - \gamma_2 \quad,		\gamma_1 = \frac{1}{A}\left[E_\mathrm{slab} - \sum_i N_i\mu_i(p, T)\right] - \gamma_2 \quad,
	~~</math>~~		\label{eqn:gen_surfen}
			\end{equation}
	where the bulk energy is replaced by a term with the chemical potentials ~~<math>~~\mu_i~~</math>~~, which influence the surface energies. Thus, the value of the temperature- and pressure-dependent chemical potential can determine which surface is energetically most favorable.		where the bulk energy is replaced by a term with the chemical potentials $\mu_i$, which influence the surface energies. Thus, the value of the temperature- and pressure-dependent chemical potential can determine which surface is energetically most favorable.
	{{NB\|tip\|The surface energy must be converged with respect to both the number of layers and the vacuum thickness. This can be challenging. To achieve good convergence of the surface energy with respect to slab thickness, it is beneficial to use a bulk cell with the same symmetry as the surface cell to ensure equivalent k-point sampling. Another approach is to infer the bulk energy from the energies of progressively thicker slabs using the Boettger method{{cite\|boettger:prb:1994}}.}}		{{NB\|tip\|The surface energy must be converged with respect to both the number of layers and the vacuum thickness. This can be challenging. To achieve good convergence of the surface energy with respect to slab thickness, it is beneficial to use a bulk cell with the same symmetry as the surface cell to ensure equivalent k-point sampling. Another approach is to infer the bulk energy from the energies of progressively thicker slabs using the Boettger method{{cite\|boettger:prb:1994}}.}}
	{{NB\|mind\|For weakly bound surfaces in large cells, it may be necessary to increase the electrostatic cutoff ({{TAG\|EWALD_CUTOFF\|6.0}}) and use reciprocal-space projectors to achieve meV-level convergence across number of layers and vacuum thickness. As reciprocal-space projectors are inefficient for large cells, first converge with {{TAG\|LREAL\|Auto}}, then restart from the converged {{FILE\|WAVECAR}} file with {{TAG\|LREAL\|FALSE}} for the final total energy.}}		{{NB\|mind\|For weakly bound surfaces in large cells, it may be necessary to increase the electrostatic cutoff ({{TAG\|EWALD_CUTOFF\|6.0}}) and use reciprocal-space projectors to achieve meV-level convergence across number of layers and vacuum thickness. As reciprocal-space projectors are inefficient for large cells, first converge with {{TAG\|LREAL\|Auto}}, then restart from the converged {{FILE\|WAVECAR}} file with {{TAG\|LREAL\|FALSE}} for the final total energy.}}

Liebetreu: /* Surface-energy calculations */

2026-04-15T07:28:58Z

Surface-energy calculations

← Older revision		Revision as of 07:28, 15 April 2026
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	<math>		<math>
	\gamma = \frac{1}{2A}\left[E_\mathrm{slab} - N E_\mathrm{bulk}\right] \quad,		\gamma = \frac{1}{2A}\left[E_\mathrm{slab} - N E_\mathrm{bulk}\right] \quad,
	<\math>		</math>

	where <math>E_\mathrm{slab}</math> is the total energy of the slab, <math>E_\mathrm{bulk}</math> is the total energy of the bulk, and <math>N</math> is the number of formula units in the slab relative to those in the bulk cell.		where <math>E_\mathrm{slab}</math> is the total energy of the slab, <math>E_\mathrm{bulk}</math> is the total energy of the bulk, and <math>N</math> is the number of formula units in the slab relative to those in the bulk cell.
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	<math>		<math>
	\gamma_1 = \frac{1}{A}\left[E_\mathrm{slab} - \sum_i N_i\mu_i(p, T)\right] - \gamma_2 \quad,		\gamma_1 = \frac{1}{A}\left[E_\mathrm{slab} - \sum_i N_i\mu_i(p, T)\right] - \gamma_2 \quad,
	~~\label{eqn:gen_surfen}~~
	</math>		</math>

Liebetreu at 07:27, 15 April 2026

2026-04-15T07:27:07Z

← Older revision		Revision as of 07:27, 15 April 2026
Line 11:		Line 11:
	Although thin-film simulations often employ the same computational setup and slab model as surface calculations, their objective differs. In thin-film studies, the goal is to investigate the behavior and properties of the entire system — including both surfaces and the bulk-like interior region — rather than isolating the characteristics of a single surface.		Although thin-film simulations often employ the same computational setup and slab model as surface calculations, their objective differs. In thin-film studies, the goal is to investigate the behavior and properties of the entire system — including both surfaces and the bulk-like interior region — rather than isolating the characteristics of a single surface.
	====2D materials====		====2D materials====
	This class of materials comprises ultrathin films consisting of only a few atomic layers. Prototypical examples include graphene, which is one atomic layer thick, and molybdenum disulfide (MoS~~$_2$~~), which consists of three atomic layers. Such materials can occur naturally as van der Waals–bonded layered crystals, but they can also be exfoliated and studied as mono-, bi-, or few-layer systems.		This class of materials comprises ultrathin films consisting of only a few atomic layers. Prototypical examples include graphene, which is one atomic layer thick, and molybdenum disulfide (MoS<sub>2</sub>), which consists of three atomic layers. Such materials can occur naturally as van der Waals–bonded layered crystals, but they can also be exfoliated and studied as mono-, bi-, or few-layer systems.

	==Slab symmetry and stoichiometry==		==Slab symmetry and stoichiometry==
Line 25:		Line 25:

	If a slab is non-symmetric, it is important to consider [[Electrostatic_corrections#Using_the_dipole_correction_for_slab_calculations\|dipole corrections]].		If a slab is non-symmetric, it is important to consider [[Electrostatic_corrections#Using_the_dipole_correction_for_slab_calculations\|dipole corrections]].
	The non-symmetric 111 NaCl slab (Fig. 2) is forming a dipole, with $Cl^{-}$ and $Na^{+}$ terminations on opposite sides of the slab. This leads to a potential gradient through the vacuum, which is not physical and leads to extra interaction between the slab replicas.		The non-symmetric 111 NaCl slab (Fig. 2) is forming a dipole, with Cl<sup>-</sup> and Na<sup>+</sup> terminations on opposite sides of the slab. This leads to a potential gradient through the vacuum, which is not physical and leads to extra interaction between the slab replicas.
	In general, this can be true for any non-symmetric slabs, not only for ionic crystals like NaCl. In those cases, dipole corrections should always be turned on and the size of the dipole checked in the {{FILE\|OUTCAR}} file. However, energy differences due to dipole interactions are usually smaller than energy differences due to a different [[exchange-correlation functional]]. They can also interfere with convergence during [[structure optimization\|relaxations]]. It is thus usually advisable to initially relax the system without dipole corrections and then turn on the corrections in a static follow-up calculation. If there is a resulting dipole, a follow-up relaxation can be performed using the {{FILE\|WAVECAR}} file from the static calculation as a starting point.		In general, this can be true for any non-symmetric slabs, not only for ionic crystals like NaCl. In those cases, dipole corrections should always be turned on and the size of the dipole checked in the {{FILE\|OUTCAR}} file. However, energy differences due to dipole interactions are usually smaller than energy differences due to a different [[exchange-correlation functional]]. They can also interfere with convergence during [[structure optimization\|relaxations]]. It is thus usually advisable to initially relax the system without dipole corrections and then turn on the corrections in a static follow-up calculation. If there is a resulting dipole, a follow-up relaxation can be performed using the {{FILE\|WAVECAR}} file from the static calculation as a starting point.

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	===Surface-energy calculations===		===Surface-energy calculations===
	The surface energy, $\gamma$, is an important characteristic of any surface, determining its stability and influencing its adhesion properties, catalytic activity, and ability to form thin films and interfaces.		The surface energy, <math>\gamma</math>, is an important characteristic of any surface, determining its stability and influencing its adhesion properties, catalytic activity, and ability to form thin films and interfaces.

	For a symmetric and stoichiometric surface slab, the surface energy $\gamma$ of the two equivalent surfaces is given by:		For a symmetric and stoichiometric surface slab, the surface energy <math>\gamma</math> of the two equivalent surfaces is given by:
	~~\begin{equation}~~
			<math>
	\gamma = \frac{1}{2A}\left[E_\mathrm{slab} - N E_\mathrm{bulk}\right] \quad,		\gamma = \frac{1}{2A}\left[E_\mathrm{slab} - N E_\mathrm{bulk}\right] \quad,
	\~~end{equation}~~		<\math>
	where $E_\mathrm{slab}$ is the total energy of the slab, $E_\mathrm{bulk}$ is the total energy of the bulk, and $N$ is the number of formula units in the slab relative to those in the bulk cell.
			where <math>E_\mathrm{slab}</math> is the total energy of the slab, <math>E_\mathrm{bulk}</math> is the total energy of the bulk, and <math>N</math> is the number of formula units in the slab relative to those in the bulk cell.

			A more general formula, that holds for non-stoichiometric and non-symmetric slabs for the surface energies <math>\gamma_1</math> and <math>\gamma_2</math> on both sides of the slab is

	~~A more general formula, that holds for non-stoichiometric and non-symmetric slabs for the surface energies $\gamma_1$ and $\gamma_2$ on both sides of the slab is~~		<math>
	~~\begin{equation}~~
	\gamma_1 = \frac{1}{A}\left[E_\mathrm{slab} - \sum_i N_i\mu_i(p, T)\right] - \gamma_2 \quad,		\gamma_1 = \frac{1}{A}\left[E_\mathrm{slab} - \sum_i N_i\mu_i(p, T)\right] - \gamma_2 \quad,
	\label{eqn:gen_surfen}		\label{eqn:gen_surfen}
	~~\end{equation}~~		</math>
	where the bulk energy is replaced by a term with the chemical potentials $\mu_i$, which influence the surface energies. Thus, the value of the temperature- and pressure-dependent chemical potential can determine which surface is energetically most favorable.
			where the bulk energy is replaced by a term with the chemical potentials <math>\mu_i</math>, which influence the surface energies. Thus, the value of the temperature- and pressure-dependent chemical potential can determine which surface is energetically most favorable.
	{{NB\|tip\|The surface energy must be converged with respect to both the number of layers and the vacuum thickness. This can be challenging. To achieve good convergence of the surface energy with respect to slab thickness, it is beneficial to use a bulk cell with the same symmetry as the surface cell to ensure equivalent k-point sampling. Another approach is to infer the bulk energy from the energies of progressively thicker slabs using the Boettger method{{cite\|boettger:prb:1994}}.}}		{{NB\|tip\|The surface energy must be converged with respect to both the number of layers and the vacuum thickness. This can be challenging. To achieve good convergence of the surface energy with respect to slab thickness, it is beneficial to use a bulk cell with the same symmetry as the surface cell to ensure equivalent k-point sampling. Another approach is to infer the bulk energy from the energies of progressively thicker slabs using the Boettger method{{cite\|boettger:prb:1994}}.}}
	{{NB\|mind\|For weakly bound surfaces in large cells, it may be necessary to increase the electrostatic cutoff ({{TAG\|EWALD_CUTOFF\|6.0}}) and use reciprocal-space projectors to achieve meV-level convergence across number of layers and vacuum thickness. As reciprocal-space projectors are inefficient for large cells, first converge with {{TAG\|LREAL\|Auto}}, then restart from the converged {{FILE\|WAVECAR}} file with {{TAG\|LREAL\|FALSE}} for the final total energy.}}		{{NB\|mind\|For weakly bound surfaces in large cells, it may be necessary to increase the electrostatic cutoff ({{TAG\|EWALD_CUTOFF\|6.0}}) and use reciprocal-space projectors to achieve meV-level convergence across number of layers and vacuum thickness. As reciprocal-space projectors are inefficient for large cells, first converge with {{TAG\|LREAL\|Auto}}, then restart from the converged {{FILE\|WAVECAR}} file with {{TAG\|LREAL\|FALSE}} for the final total energy.}}

Wolloch: /* Surface-energy calculations */

2026-03-30T06:47:02Z

Surface-energy calculations

← Older revision		Revision as of 06:47, 30 March 2026
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	where the bulk energy is replaced by a term with the chemical potentials $\mu_i$, which influence the surface energies. Thus, the value of the temperature- and pressure-dependent chemical potential can determine which surface is energetically most favorable.		where the bulk energy is replaced by a term with the chemical potentials $\mu_i$, which influence the surface energies. Thus, the value of the temperature- and pressure-dependent chemical potential can determine which surface is energetically most favorable.
	{{NB\|tip\|The surface energy must be converged with respect to both the number of layers and the vacuum thickness. This can be challenging. To achieve good convergence of the surface energy with respect to slab thickness, it is beneficial to use a bulk cell with the same symmetry as the surface cell to ensure equivalent k-point sampling. Another approach is to infer the bulk energy from the energies of progressively thicker slabs using the Boettger method{{cite\|boettger:prb:1994}}.}}		{{NB\|tip\|The surface energy must be converged with respect to both the number of layers and the vacuum thickness. This can be challenging. To achieve good convergence of the surface energy with respect to slab thickness, it is beneficial to use a bulk cell with the same symmetry as the surface cell to ensure equivalent k-point sampling. Another approach is to infer the bulk energy from the energies of progressively thicker slabs using the Boettger method{{cite\|boettger:prb:1994}}.}}
	~~<!--~~
	{{NB\|mind\|For weakly bound surfaces in large cells, it may be necessary to increase the electrostatic cutoff ({{TAG\|EWALD_CUTOFF\|6.0}}) and use reciprocal-space projectors to achieve meV-level convergence across number of layers and vacuum thickness. As reciprocal-space projectors are inefficient for large cells, first converge with {{TAG\|LREAL\|Auto}}, then restart from the converged {{FILE\|WAVECAR}} file with {{TAG\|LREAL\|FALSE}} for the final total energy.}}		{{NB\|mind\|For weakly bound surfaces in large cells, it may be necessary to increase the electrostatic cutoff ({{TAG\|EWALD_CUTOFF\|6.0}}) and use reciprocal-space projectors to achieve meV-level convergence across number of layers and vacuum thickness. As reciprocal-space projectors are inefficient for large cells, first converge with {{TAG\|LREAL\|Auto}}, then restart from the converged {{FILE\|WAVECAR}} file with {{TAG\|LREAL\|FALSE}} for the final total energy.}}
	~~-->~~

	Please also consult our [https://www.vasp.at/tutorials/latest/surface/part1/ tutorial on Ni(111)] for more in-depth information about surface-energy calculations.		Please also consult our [https://www.vasp.at/tutorials/latest/surface/part1/ tutorial on Ni(111)] for more in-depth information about surface-energy calculations.

Wolloch: /* Surface-energy calculations */

2026-03-17T09:49:36Z

Surface-energy calculations

← Older revision		Revision as of 09:49, 17 March 2026
Line 78:		Line 78:
	where the bulk energy is replaced by a term with the chemical potentials $\mu_i$, which influence the surface energies. Thus, the value of the temperature- and pressure-dependent chemical potential can determine which surface is energetically most favorable.		where the bulk energy is replaced by a term with the chemical potentials $\mu_i$, which influence the surface energies. Thus, the value of the temperature- and pressure-dependent chemical potential can determine which surface is energetically most favorable.
	{{NB\|tip\|The surface energy must be converged with respect to both the number of layers and the vacuum thickness. This can be challenging. To achieve good convergence of the surface energy with respect to slab thickness, it is beneficial to use a bulk cell with the same symmetry as the surface cell to ensure equivalent k-point sampling. Another approach is to infer the bulk energy from the energies of progressively thicker slabs using the Boettger method{{cite\|boettger:prb:1994}}.}}		{{NB\|tip\|The surface energy must be converged with respect to both the number of layers and the vacuum thickness. This can be challenging. To achieve good convergence of the surface energy with respect to slab thickness, it is beneficial to use a bulk cell with the same symmetry as the surface cell to ensure equivalent k-point sampling. Another approach is to infer the bulk energy from the energies of progressively thicker slabs using the Boettger method{{cite\|boettger:prb:1994}}.}}
			<!--
			{{NB\|mind\|For weakly bound surfaces in large cells, it may be necessary to increase the electrostatic cutoff ({{TAG\|EWALD_CUTOFF\|6.0}}) and use reciprocal-space projectors to achieve meV-level convergence across number of layers and vacuum thickness. As reciprocal-space projectors are inefficient for large cells, first converge with {{TAG\|LREAL\|Auto}}, then restart from the converged {{FILE\|WAVECAR}} file with {{TAG\|LREAL\|FALSE}} for the final total energy.}}
			-->

	Please also consult our [https://www.vasp.at/tutorials/latest/surface/part1/ tutorial on Ni(111)] for more in-depth information about surface-energy calculations.		Please also consult our [https://www.vasp.at/tutorials/latest/surface/part1/ tutorial on Ni(111)] for more in-depth information about surface-energy calculations.

Huebsch at 11:07, 3 November 2025

2025-11-03T11:07:15Z

← Older revision		Revision as of 11:07, 3 November 2025
Line 1:		Line 1:
			= Surfaces, thin films, and 2D materials =
	Every real crystal or material has a '''surface'''. In VASP simulations, however, periodic boundary conditions typically model an infinite crystal, the perfect bulk.		Every real crystal or material has a '''surface'''. In VASP simulations, however, periodic boundary conditions typically model an infinite crystal, the perfect bulk.
	To model a '''surface''', a '''thin film''', or an intrinsically '''2D material''', therefore, requires breaking these periodic boundary conditions intentionally. This is done by elongating the simulation cell in one direction (normal to the intended surface) without adding more atoms. This creates a vacuum region between repeated images of thin films of material (commonly called surface slabs, or just slabs), each of which has two surfaces.		To model a '''surface''', a '''thin film''', or an intrinsically '''2D material''', therefore, requires breaking these periodic boundary conditions intentionally. This is done by elongating the simulation cell in one direction (normal to the intended surface) without adding more atoms. This creates a vacuum region between repeated images of thin films of material (commonly called surface slabs, or just slabs), each of which has two surfaces.

Wolloch: /* Advice and recommendations */

2025-10-23T12:40:50Z

Advice and recommendations

← Older revision		Revision as of 12:40, 23 October 2025
Line 57:		Line 57:

	===Out-of-plane lattice parameters===		===Out-of-plane lattice parameters===
	Since bonds will be cut when a surface is created, the spacing between the first two layers of the surface will usually be reduced, with respect to the bulk lattice spacing. This effect is often important for the surface properties and should not be disregarded.		Since bonds will be cut when a surface is created, the spacing between the first two layers of the surface will usually be reduced with respect to the bulk lattice spacing. This effect is often important for the surface properties and should not be disregarded.
	Avoiding this relaxation on the slab side opposite to the surface of interest, however, can reduce the total number of layers needed to mimic the semi-infinite bulk.		Avoiding this relaxation on the slab side opposite to the surface of interest, however, can reduce the total number of layers needed to mimic the semi-infinite bulk.
	{{NB\|tip\|For a surface calculation, it is often beneficial to fix several layers at the bottom of the slab to simulate the semi-infinite bulk more efficiently and with fewer total layers. The [[POSCAR#poscar6\|Selective Dynamics]] options in the {{FILE\|POSCAR}} file can be used for this purpose. A thin film should be fully relaxed.}}		{{NB\|tip\|For a surface calculation, it is often beneficial to fix several layers at the bottom of the slab to simulate the semi-infinite bulk more efficiently and with fewer total layers. The [[POSCAR#poscar6\|Selective Dynamics]] options in the {{FILE\|POSCAR}} file can be used for this purpose. A thin film should be fully relaxed.}}
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	Scanning-tunneling-microscopy (STM) pictures can be simulated by using a post-processing method to compute partial charge densities.		Scanning-tunneling-microscopy (STM) pictures can be simulated by using a post-processing method to compute partial charge densities.
	Please consult our how-to page on [[partial charge densities and STM simulations]].		Please consult our how-to page on [[partial charge densities and STM simulations]].

			=== Electrostatic corrections ===

			As mentioned, e.g., in the [[#Slab_symmetry\|slab symmetry]] or [[#Adsorption_at_a_surface\|adsorption at a surface]] sections, electrostatic corrections can be important for 2D materials, thin films, and surfaces. Please consult the [[:Category:electrostatics\|electrostatics]] and the [[electrostatic corrections]] pages for more information.

	== Tutorials ==		== Tutorials ==

Wolloch: /* Slab symmetry */

2025-10-23T12:30:41Z

Slab symmetry

← Older revision		Revision as of 12:30, 23 October 2025
Line 25:		Line 25:
	If a slab is non-symmetric, it is important to consider [[Electrostatic_corrections#Using_the_dipole_correction_for_slab_calculations\|dipole corrections]].		If a slab is non-symmetric, it is important to consider [[Electrostatic_corrections#Using_the_dipole_correction_for_slab_calculations\|dipole corrections]].
	The non-symmetric 111 NaCl slab (Fig. 2) is forming a dipole, with $Cl^{-}$ and $Na^{+}$ terminations on opposite sides of the slab. This leads to a potential gradient through the vacuum, which is not physical and leads to extra interaction between the slab replicas.		The non-symmetric 111 NaCl slab (Fig. 2) is forming a dipole, with $Cl^{-}$ and $Na^{+}$ terminations on opposite sides of the slab. This leads to a potential gradient through the vacuum, which is not physical and leads to extra interaction between the slab replicas.
	In general, this can be true for any non-symmetric slabs, not only for ionic crystals like NaCl. In those cases, dipole corrections should always be turned on and the size of the dipole checked in the {{FILE\|OUTCAR}} file. However, energy differences due to dipole interactions are usually smaller than energy differences due to a different [[exchange-correlation functional]]. They can also interfere with convergence during [[structure optimization\|relaxations]]. It is thus usually advisable to initially relax the system without dipole corrections and then turn on the corrections in a static follow-up calculation ~~and proceed based on~~ the ~~size of~~ the ~~effect~~.		In general, this can be true for any non-symmetric slabs, not only for ionic crystals like NaCl. In those cases, dipole corrections should always be turned on and the size of the dipole checked in the {{FILE\|OUTCAR}} file. However, energy differences due to dipole interactions are usually smaller than energy differences due to a different [[exchange-correlation functional]]. They can also interfere with convergence during [[structure optimization\|relaxations]]. It is thus usually advisable to initially relax the system without dipole corrections and then turn on the corrections in a static follow-up calculation. If there is a resulting dipole, a follow-up relaxation can be performed using the {{FILE\|WAVECAR}} file from the static calculation as a starting point.

	Slab symmetry is also important for surface calculations. If the two surfaces of a slab are not equal, the [[#surface-energy calculations\|computation of the surface energy]] becomes more cumbersome.		Slab symmetry is also important for surface calculations. If the two surfaces of a slab are not equal, the [[#surface-energy calculations\|computation of the surface energy]] becomes more cumbersome.

Huebsch at 10:28, 23 October 2025

2025-10-23T10:28:13Z

← Older revision		Revision as of 10:28, 23 October 2025
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	== References ==		== References ==

	[[~~Catregory~~:Symmetry]]		[[Category:Symmetry]]

Huebsch: Huebsch moved page Construction:Surfaces, thin films, and 2D materials to Category:2D materials without leaving a redirect

2025-10-23T10:26:22Z

Huebsch moved page Construction:Surfaces, thin films, and 2D materials to Category:2D materials without leaving a redirect

← Older revision	Revision as of 10:26, 23 October 2025
(No difference)