Volume relaxation - Revision history

Csheldon: /* 2. Equation of state fitting */

2025-11-03T13:21:39Z

2. Equation of state fitting

← Older revision		Revision as of 13:21, 3 November 2025
Line 63:		Line 63:

	== 2. Equation of state fitting ==		== 2. Equation of state fitting ==
	An alternative way to avoid relaxing the volume is to relax the ionic positions and cell shape for a fixed set of volumes, i.e., multiple {{TAG\|POSCAR}} files. These are then fitted to an equation of state (EOS), e.g., Murnaghan {{cite\|murnaghan:web}}. As the Pulay stress is almost isotropic, only a constant value is added to the diagonal elements of the stress tensor <ref>One thing which is important to understand is that problems due to the Pulay stress can often be neglected if only volume conserving relaxations are performed. This is because the Pulay stress is usually almost uniform and it, therefore, changes the diagonal elements of the stress tensor only by a certain constant amount (see below). In addition, many calculations have shown that Pulay stress-related problems can also be reduced by performing calculations at different volumes using the same energy cutoff for each calculation (this is what VASP does by default) and fitting the final energies to an equation of state. This of course implies that the number of basis vectors is different at each volume. Calculations with many plane-wave codes have shown that such calculations yield reliable results for the lattice constants and the bulk modulus and other elastic properties even at relatively modest energy cutoffs. Constant energy cut-off calculations are less prone to errors caused by the basis set incompleteness than constant basis set calculations. But it should be kept in mind that volume changes and cell shape changes must be rather large in order to obtain reliable results from this method because within the limit of very small distortions the energy changes obtained with this method are equivalent to those obtained from the stress tensor and are therefore affected by the Pulay stress. Only volume changes of the order of 5-10 % guarantee that the errors introduced by the basis set incompleteness are averaged out.</ref>. Therefore, the relaxation for a fixed volume will yield highly accurate structures. This approach has the advantage of also providing the bulk modulus, and we have found it may be used safely with the default energy cutoff.		An alternative way to avoid relaxing the volume is to relax the ionic positions and cell shape for a fixed set of volumes, i.e., multiple {{TAG\|POSCAR}} files. These are then fitted to an equation of state (EOS), e.g., Murnaghan {{cite\|murnaghan:web}}. As the Pulay stress is almost isotropic, only a constant value is added to the diagonal elements of the stress tensor. Therefore, the relaxation for a fixed volume will yield highly accurate structures. This approach has the advantage of also providing the bulk modulus, and we have found it may be used safely with the default energy cutoff.

	To fit the equation of state, you need to do calculations for a set of fixed volumes. The following steps are required:		To fit the equation of state, you need to do calculations for a set of fixed volumes <ref>This, of course, implies that the number of basis vectors is different at each volume. Calculations with many plane-wave codes have shown that such calculations yield reliable results for the lattice constants and the bulk modulus and other elastic properties even at relatively modest energy cutoffs. Constant energy cut-off calculations are less prone to errors caused by the basis set incompleteness than constant basis set calculations. But it should be kept in mind that volume and cell shape changes must be rather large in order to obtain reliable results from this method, because within the limit of very small distortions, the energy changes obtained with this method are equivalent to those obtained from the stress tensor and are therefore affected by the Pulay stress. Only volume changes of the order of 5-10 % guarantee that the errors introduced by the basis set incompleteness are averaged out.</ref>. The following steps are required:

	=== Step 0. ===		=== Step 0. ===

Csheldon: /* 2. Equation of state fitting */

2025-11-03T13:19:00Z

2. Equation of state fitting

← Older revision		Revision as of 13:19, 3 November 2025
Line 63:		Line 63:

	== 2. Equation of state fitting ==		== 2. Equation of state fitting ==
	An alternative way to avoid relaxing the volume is to relax the ionic positions and cell shape for a fixed set of volumes, i.e., multiple {{TAG\|POSCAR}} files. These are then fitted to an equation of state (EOS), e.g., Murnaghan {{cite\|murnaghan:web}}. As the Pulay stress is almost isotropic, only a constant value is added to the diagonal elements of the stress tensor <ref>~~Side remark~~</ref>. Therefore, the relaxation for a fixed volume will yield highly accurate structures. This approach has the advantage of also providing the bulk modulus, and we have found it may be used safely with the default energy cutoff.		An alternative way to avoid relaxing the volume is to relax the ionic positions and cell shape for a fixed set of volumes, i.e., multiple {{TAG\|POSCAR}} files. These are then fitted to an equation of state (EOS), e.g., Murnaghan {{cite\|murnaghan:web}}. As the Pulay stress is almost isotropic, only a constant value is added to the diagonal elements of the stress tensor <ref>One thing which is important to understand is that problems due to the Pulay stress can often be neglected if only volume conserving relaxations are performed. This is because the Pulay stress is usually almost uniform and it, therefore, changes the diagonal elements of the stress tensor only by a certain constant amount (see below). In addition, many calculations have shown that Pulay stress-related problems can also be reduced by performing calculations at different volumes using the same energy cutoff for each calculation (this is what VASP does by default) and fitting the final energies to an equation of state. This of course implies that the number of basis vectors is different at each volume. Calculations with many plane-wave codes have shown that such calculations yield reliable results for the lattice constants and the bulk modulus and other elastic properties even at relatively modest energy cutoffs. Constant energy cut-off calculations are less prone to errors caused by the basis set incompleteness than constant basis set calculations. But it should be kept in mind that volume changes and cell shape changes must be rather large in order to obtain reliable results from this method because within the limit of very small distortions the energy changes obtained with this method are equivalent to those obtained from the stress tensor and are therefore affected by the Pulay stress. Only volume changes of the order of 5-10 % guarantee that the errors introduced by the basis set incompleteness are averaged out.</ref>. Therefore, the relaxation for a fixed volume will yield highly accurate structures. This approach has the advantage of also providing the bulk modulus, and we have found it may be used safely with the default energy cutoff.

	To fit the equation of state, you need to do calculations for a set of fixed volumes. The following steps are required:		To fit the equation of state, you need to do calculations for a set of fixed volumes. The following steps are required:

Csheldon: /* 2. Equation of state fitting */

2025-11-03T13:18:33Z

2. Equation of state fitting

← Older revision		Revision as of 13:18, 3 November 2025
Line 63:		Line 63:

	== 2. Equation of state fitting ==		== 2. Equation of state fitting ==
	An alternative way to avoid relaxing the volume is to relax the ionic positions and cell shape for a fixed set of volumes, i.e., multiple {{TAG\|POSCAR}} files. These are then fitted to an equation of state (EOS), e.g., Murnaghan {{cite\|murnaghan:web}}. As the Pulay stress is almost isotropic, only a constant value is added to the diagonal elements of the stress tensor. Therefore, the relaxation for a fixed volume will yield highly accurate structures. This approach has the advantage of also providing the bulk modulus, and we have found it may be used safely with the default energy cutoff.		An alternative way to avoid relaxing the volume is to relax the ionic positions and cell shape for a fixed set of volumes, i.e., multiple {{TAG\|POSCAR}} files. These are then fitted to an equation of state (EOS), e.g., Murnaghan {{cite\|murnaghan:web}}. As the Pulay stress is almost isotropic, only a constant value is added to the diagonal elements of the stress tensor <ref>Side remark</ref>. Therefore, the relaxation for a fixed volume will yield highly accurate structures. This approach has the advantage of also providing the bulk modulus, and we have found it may be used safely with the default energy cutoff.

	To fit the equation of state, you need to do calculations for a set of fixed volumes. The following steps are required:		To fit the equation of state, you need to do calculations for a set of fixed volumes. The following steps are required:

Csheldon: /* 2. Equation of state fitting */

2025-11-03T13:14:23Z

2. Equation of state fitting

← Older revision		Revision as of 13:14, 3 November 2025
Line 63:		Line 63:

	== 2. Equation of state fitting ==		== 2. Equation of state fitting ==
	An alternative way to avoid relaxing the volume is to relax the ionic positions and cell shape for a fixed set of volumes, i.e., multiple {{TAG\|POSCAR}} files. These are then fitted to an equation of state, e.g., Murnaghan {{cite\|murnaghan:web}}. As the Pulay stress is almost isotropic, only a constant value is added to the diagonal elements of the stress tensor. Therefore, the relaxation for a fixed volume will yield highly accurate structures. This approach has the advantage of also providing the bulk modulus, and we have found it may be used safely with the default energy cutoff.		An alternative way to avoid relaxing the volume is to relax the ionic positions and cell shape for a fixed set of volumes, i.e., multiple {{TAG\|POSCAR}} files. These are then fitted to an equation of state (EOS), e.g., Murnaghan {{cite\|murnaghan:web}}. As the Pulay stress is almost isotropic, only a constant value is added to the diagonal elements of the stress tensor. Therefore, the relaxation for a fixed volume will yield highly accurate structures. This approach has the advantage of also providing the bulk modulus, and we have found it may be used safely with the default energy cutoff.

	This of course implies that the number of basis vectors is different at each volume. Calculations with many plane-wave codes have shown that such calculations yield reliable results for the lattice constants and the bulk modulus and other elastic properties even at relatively modest energy cutoffs. Constant energy cut-off calculations are less prone to errors caused by the basis set incompleteness than constant basis set calculations. But it should be kept in mind that volume changes and cell shape changes must be rather large in order to obtain reliable results from this method because within the limit of very small distortions the energy changes obtained with this method are equivalent to those obtained from the stress tensor and are therefore affected by the Pulay stress. Only volume changes of the order of 5-10 % guarantee that the errors introduced by the basis set incompleteness are averaged out.

	To fit the equation of state, you need to do calculations for a set of fixed volumes. The following steps are required:		To fit the equation of state, you need to do calculations for a set of fixed volumes. The following steps are required:
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	[[File:murnaghan_fit.png\|400px\|thumb\|left\|Figure 3. Murnaghan fit of 5 different lattice parameters for C diamond.]]		[[File:murnaghan_fit.png\|400px\|thumb\|left\|Figure 3. Murnaghan fit of 5 different lattice parameters for C diamond.]]
	<div style="clear:both;"></div>		<div style="clear:both;"></div>

			In the above script, we have defined Murnaghan fit explicitly. Other tools, e.g., [https://pymatgen.org/pymatgen.analysis.html#module-pymatgen.analysis.eos pymatgen], are available where EOS have been defined.

	The optimized lattice parameter is the minimum of the Murnaghan fit. Five points are used here as an example; we recommend using more to improve the fit. Take a look at our tutorials for an alternative approach where [https://www.vasp.at/tutorials/latest/bulk/part1/ a range of lattice parameters are taken for silicon].		The optimized lattice parameter is the minimum of the Murnaghan fit. Five points are used here as an example; we recommend using more to improve the fit. Take a look at our tutorials for an alternative approach where [https://www.vasp.at/tutorials/latest/bulk/part1/ a range of lattice parameters are taken for silicon].

Csheldon: /* 2. Equation of state fitting */

2025-11-03T13:05:58Z

2. Equation of state fitting

← Older revision		Revision as of 13:05, 3 November 2025
Line 64:		Line 64:
	== 2. Equation of state fitting ==		== 2. Equation of state fitting ==
	An alternative way to avoid relaxing the volume is to relax the ionic positions and cell shape for a fixed set of volumes, i.e., multiple {{TAG\|POSCAR}} files. These are then fitted to an equation of state, e.g., Murnaghan {{cite\|murnaghan:web}}. As the Pulay stress is almost isotropic, only a constant value is added to the diagonal elements of the stress tensor. Therefore, the relaxation for a fixed volume will yield highly accurate structures. This approach has the advantage of also providing the bulk modulus, and we have found it may be used safely with the default energy cutoff.		An alternative way to avoid relaxing the volume is to relax the ionic positions and cell shape for a fixed set of volumes, i.e., multiple {{TAG\|POSCAR}} files. These are then fitted to an equation of state, e.g., Murnaghan {{cite\|murnaghan:web}}. As the Pulay stress is almost isotropic, only a constant value is added to the diagonal elements of the stress tensor. Therefore, the relaxation for a fixed volume will yield highly accurate structures. This approach has the advantage of also providing the bulk modulus, and we have found it may be used safely with the default energy cutoff.

			This of course implies that the number of basis vectors is different at each volume. Calculations with many plane-wave codes have shown that such calculations yield reliable results for the lattice constants and the bulk modulus and other elastic properties even at relatively modest energy cutoffs. Constant energy cut-off calculations are less prone to errors caused by the basis set incompleteness than constant basis set calculations. But it should be kept in mind that volume changes and cell shape changes must be rather large in order to obtain reliable results from this method because within the limit of very small distortions the energy changes obtained with this method are equivalent to those obtained from the stress tensor and are therefore affected by the Pulay stress. Only volume changes of the order of 5-10 % guarantee that the errors introduced by the basis set incompleteness are averaged out.

	To fit the equation of state, you need to do calculations for a set of fixed volumes. The following steps are required:		To fit the equation of state, you need to do calculations for a set of fixed volumes. The following steps are required:

Csheldon: /* Step 4. */

2025-11-03T13:02:59Z

Step 4.

← Older revision		Revision as of 13:02, 3 November 2025
Line 154:		Line 154:
	</div>		</div>

	[[File:murnaghan_fit.png\|400px\|thumb\|left\|Murnaghan fit of 5 different lattice parameters for C diamond.]]		[[File:murnaghan_fit.png\|400px\|thumb\|left\|Figure 3. Murnaghan fit of 5 different lattice parameters for C diamond.]]
	<div style="clear:both;"></div>		<div style="clear:both;"></div>

Csheldon: /* Step 4b. */

2025-11-03T13:02:25Z

Step 4b.

← Older revision		Revision as of 13:02, 3 November 2025
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	difference in pressure = -1215.66 kB		difference in pressure = -1215.66 kB
	<ol type = 'i' start = "4">		<ol type = 'i' start = "4">
	<li>Set {{TAG\|PSTRESS}} equal to this difference in the OUTCAR file, i.e.:		<li>Set {{TAG\|PSTRESS}} equal to this difference in the {{FILE\|OUTCAR}} file, i.e.:
	</li>		</li>
	</ol>		</ol>

Csheldon: /* Step 2. */

2025-11-03T13:02:01Z

Step 2.

← Older revision		Revision as of 13:02, 3 November 2025
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	{{TAGBL\|ISIF}} = 7 ; {{TAGBL\|IBRION}} = 2; {{TAGBL\|NSW}} = 20		{{TAGBL\|ISIF}} = 7 ; {{TAGBL\|IBRION}} = 2; {{TAGBL\|NSW}} = 20
	{{TAGBL\|ISTART}} = 1 # this keeps that energy cut-off constant, while updating the plane wave basis for the new cell volume		{{TAGBL\|ISTART}} = 1 # this keeps that energy cut-off constant, while updating the plane wave basis for the new cell volume
	{{NB\|mind\| In this procedure, it is important to set {{TAG\|ISTART}} {{=}} 1 so that the basis is updated and the energy cut-off remains constant. If {{TAG\|ISTART}} {{=}} 2, the basis remains constant, which will also keep the artificial, Pulay stress, i.e. it is an exact restart of the calculation in Step 1, with identically poor settings. }}		{{NB\|mind\| In this procedure, it is important to set {{TAG\|ISTART}} {{=}} 1 so that the basis is updated and the energy cut-off remains constant. If {{TAG\|ISTART}} {{=}} 2, the basis remains constant, which will also keep the artificial, Pulay stress, i.e., it is an exact restart of the calculation in Step 1, with identically poor settings. }}

	=== Step 3. ===		=== Step 3. ===

Csheldon: /* Step 2. */

2025-11-03T13:01:50Z

Step 2.

← Older revision		Revision as of 13:01, 3 November 2025
Line 27:		Line 27:
	{{TAGBL\|ISIF}} = 7 ; {{TAGBL\|IBRION}} = 2; {{TAGBL\|NSW}} = 20		{{TAGBL\|ISIF}} = 7 ; {{TAGBL\|IBRION}} = 2; {{TAGBL\|NSW}} = 20
	{{TAGBL\|ISTART}} = 1 # this keeps that energy cut-off constant, while updating the plane wave basis for the new cell volume		{{TAGBL\|ISTART}} = 1 # this keeps that energy cut-off constant, while updating the plane wave basis for the new cell volume
	{{NB\|mind\| In this procedure, it is important to set {{TAG\|ISTART}} {{=}} 1 so that the basis is updated and the energy cut-off remains constant. If {{TAG\|ISTART}} {{=}} 2, the basis remains constant, which will also keep the artificial, Pulay, stress, i.e. it is an exact restart of the calculation in Step 1, with identically poor settings. }}		{{NB\|mind\| In this procedure, it is important to set {{TAG\|ISTART}} {{=}} 1 so that the basis is updated and the energy cut-off remains constant. If {{TAG\|ISTART}} {{=}} 2, the basis remains constant, which will also keep the artificial, Pulay stress, i.e. it is an exact restart of the calculation in Step 1, with identically poor settings. }}

	=== Step 3. ===		=== Step 3. ===

Csheldon: /* 1. Volume relaxation */

2025-11-03T13:01:00Z

1. Volume relaxation

← Older revision		Revision as of 13:01, 3 November 2025
Line 19:		Line 19:
	=== Step 1. ===		=== Step 1. ===
	Relax from the starting structure ({{TAG\|ISIF}} = 7; {{TAG\|IBRION}} = 1, 2, or 3) with Gaussian or Methfessel-Paxton smearing ({{TAG\|ISMEAR}} = 0 or 1). Note: other settings can be used for {{TAG\|ISIF}}, e.g. 3, 6, or 8 but it is not recommended to relax more than one degree of freedom at a time. For instance,		Relax from the starting structure ({{TAG\|ISIF}} = 7; {{TAG\|IBRION}} = 1, 2, or 3) with Gaussian or Methfessel-Paxton smearing ({{TAG\|ISMEAR}} = 0 or 1). Note: other settings can be used for {{TAG\|ISIF}}, e.g. 3, 6, or 8 but it is not recommended to relax more than one degree of freedom at a time. For instance,
	{{~~TAG~~\|ISMEAR}} = 0 ; {{~~TAG~~\|SIGMA}} = 0.05 # change smearing to {{~~TAG~~\|ISMEAR}} = 1 ; {{~~TAG~~\|SIGMA}} = 0.2 for metals		{{TAGBL\|ISMEAR}} = 0 ; {{TAGBL\|SIGMA}} = 0.05 # change smearing to {{TAGBL\|ISMEAR}} = 1 ; {{TAGBL\|SIGMA}} = 0.2 for metals
	{{~~TAG~~\|ISIF}} = 7 ; {{~~TAG~~\|IBRION}} = 2; {{~~TAG~~\|NSW}} = 20		{{TAGBL\|ISIF}} = 7 ; {{TAGBL\|IBRION}} = 2; {{TAGBL\|NSW}} = 20

	=== Step 2. ===		=== Step 2. ===
	Copy the {{TAG\|CONTCAR}} to {{TAG\|POSCAR}} and relax the structure again.		Copy the {{TAG\|CONTCAR}} to {{TAG\|POSCAR}} and relax the structure again.
	{{~~TAG~~\|ISMEAR}} = 0 ; {{~~TAG~~\|SIGMA}} = 0.05 # change smearing to {{~~TAG~~\|ISMEAR}} = 1 ; {{~~TAG~~\|SIGMA}} = 0.2 for metals		{{TAGBL\|ISMEAR}} = 0 ; {{TAGBL\|SIGMA}} = 0.05 # change smearing to {{TAGBL\|ISMEAR}} = 1 ; {{TAGBL\|SIGMA}} = 0.2 for metals
	{{~~TAG~~\|ISIF}} = 7 ; {{~~TAG~~\|IBRION}} = 2; {{~~TAG~~\|NSW}} = 20		{{TAGBL\|ISIF}} = 7 ; {{TAGBL\|IBRION}} = 2; {{TAGBL\|NSW}} = 20
	{{~~TAG~~\|ISTART}} = 1 # this keeps that energy cut-off constant, while updating the plane wave basis for the new cell volume		{{TAGBL\|ISTART}} = 1 # this keeps that energy cut-off constant, while updating the plane wave basis for the new cell volume
	{{NB\|mind\| In this procedure, it is important to set {{TAG\|ISTART}} {{=}} 1 so that the basis is updated and the energy cut-off remains constant. If {{TAG\|ISTART}} {{=}} 2, the basis remains constant, which will also keep the artificial, Pulay, stress, i.e. it is an exact restart of the calculation in Step 1, with identically poor settings. }}		{{NB\|mind\| In this procedure, it is important to set {{TAG\|ISTART}} {{=}} 1 so that the basis is updated and the energy cut-off remains constant. If {{TAG\|ISTART}} {{=}} 2, the basis remains constant, which will also keep the artificial, Pulay, stress, i.e. it is an exact restart of the calculation in Step 1, with identically poor settings. }}

	=== Step 3. ===		=== Step 3. ===
	Change the smearing method to the tetrahedron method (i.e. {{TAG\|ISMEAR}}=-5) and perform a single point calculation, i.e. no relaxation of structure. These will give highly accurate energies.		Change the smearing method to the tetrahedron method (i.e. {{TAG\|ISMEAR}}=-5) and perform a single point calculation, i.e. no relaxation of structure. These will give highly accurate energies.
	{{~~TAG~~\|ISMEAR}} = -5 # tetrahedron method		{{TAGBL\|ISMEAR}} = -5 # tetrahedron method
	{{~~TAG~~\|NSW}} = 0		{{TAGBL\|NSW}} = 0

	=== (Optional) ===		=== (Optional) ===
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	</li>		</li>
	</ol>		</ol>
	{{~~TAG~~\|PSTRESS}} = -1215.66		{{TAGBL\|PSTRESS}} = -1215.66
	This results in structures similar to the higher cutoff at the cost of the default cutoff. We reiterate that {{TAG\|PSTRESS}} should only be used if the higher cutoff is not a viable option, as this only improves the structure and not the energy.		This results in structures similar to the higher cutoff at the cost of the default cutoff. We reiterate that {{TAG\|PSTRESS}} should only be used if the higher cutoff is not a viable option, as this only improves the structure and not the energy.

← Older revision		Revision as of 13:01, 3 November 2025
Line 19:		Line 19:
	=== Step 1. ===		=== Step 1. ===
	Relax from the starting structure ({{TAG\|ISIF}} = 7; {{TAG\|IBRION}} = 1, 2, or 3) with Gaussian or Methfessel-Paxton smearing ({{TAG\|ISMEAR}} = 0 or 1). Note: other settings can be used for {{TAG\|ISIF}}, e.g. 3, 6, or 8 but it is not recommended to relax more than one degree of freedom at a time. For instance,		Relax from the starting structure ({{TAG\|ISIF}} = 7; {{TAG\|IBRION}} = 1, 2, or 3) with Gaussian or Methfessel-Paxton smearing ({{TAG\|ISMEAR}} = 0 or 1). Note: other settings can be used for {{TAG\|ISIF}}, e.g. 3, 6, or 8 but it is not recommended to relax more than one degree of freedom at a time. For instance,
	{{~~TAG~~\|ISMEAR}} = 0 ; {{~~TAG~~\|SIGMA}} = 0.05 # change smearing to {{~~TAG~~\|ISMEAR}} = 1 ; {{~~TAG~~\|SIGMA}} = 0.2 for metals		{{TAGBL\|ISMEAR}} = 0 ; {{TAGBL\|SIGMA}} = 0.05 # change smearing to {{TAGBL\|ISMEAR}} = 1 ; {{TAGBL\|SIGMA}} = 0.2 for metals
	{{~~TAG~~\|ISIF}} = 7 ; {{~~TAG~~\|IBRION}} = 2; {{~~TAG~~\|NSW}} = 20		{{TAGBL\|ISIF}} = 7 ; {{TAGBL\|IBRION}} = 2; {{TAGBL\|NSW}} = 20

	=== Step 2. ===		=== Step 2. ===
	Copy the {{TAG\|CONTCAR}} to {{TAG\|POSCAR}} and relax the structure again.		Copy the {{TAG\|CONTCAR}} to {{TAG\|POSCAR}} and relax the structure again.
	{{~~TAG~~\|ISMEAR}} = 0 ; {{~~TAG~~\|SIGMA}} = 0.05 # change smearing to {{~~TAG~~\|ISMEAR}} = 1 ; {{~~TAG~~\|SIGMA}} = 0.2 for metals		{{TAGBL\|ISMEAR}} = 0 ; {{TAGBL\|SIGMA}} = 0.05 # change smearing to {{TAGBL\|ISMEAR}} = 1 ; {{TAGBL\|SIGMA}} = 0.2 for metals
	{{~~TAG~~\|ISIF}} = 7 ; {{~~TAG~~\|IBRION}} = 2; {{~~TAG~~\|NSW}} = 20		{{TAGBL\|ISIF}} = 7 ; {{TAGBL\|IBRION}} = 2; {{TAGBL\|NSW}} = 20
	{{~~TAG~~\|ISTART}} = 1 # this keeps that energy cut-off constant, while updating the plane wave basis for the new cell volume		{{TAGBL\|ISTART}} = 1 # this keeps that energy cut-off constant, while updating the plane wave basis for the new cell volume
	{{NB\|mind\| In this procedure, it is important to set {{TAG\|ISTART}} {{=}} 1 so that the basis is updated and the energy cut-off remains constant. If {{TAG\|ISTART}} {{=}} 2, the basis remains constant, which will also keep the artificial, Pulay, stress, i.e. it is an exact restart of the calculation in Step 1, with identically poor settings. }}		{{NB\|mind\| In this procedure, it is important to set {{TAG\|ISTART}} {{=}} 1 so that the basis is updated and the energy cut-off remains constant. If {{TAG\|ISTART}} {{=}} 2, the basis remains constant, which will also keep the artificial, Pulay, stress, i.e. it is an exact restart of the calculation in Step 1, with identically poor settings. }}

	=== Step 3. ===		=== Step 3. ===
	Change the smearing method to the tetrahedron method (i.e. {{TAG\|ISMEAR}}=-5) and perform a single point calculation, i.e. no relaxation of structure. These will give highly accurate energies.		Change the smearing method to the tetrahedron method (i.e. {{TAG\|ISMEAR}}=-5) and perform a single point calculation, i.e. no relaxation of structure. These will give highly accurate energies.
	{{~~TAG~~\|ISMEAR}} = -5 # tetrahedron method		{{TAGBL\|ISMEAR}} = -5 # tetrahedron method
	{{~~TAG~~\|NSW}} = 0		{{TAGBL\|NSW}} = 0

	=== (Optional) ===		=== (Optional) ===
Line 59:		Line 59:
	</li>		</li>
	</ol>		</ol>
	{{~~TAG~~\|PSTRESS}} = -1215.66		{{TAGBL\|PSTRESS}} = -1215.66
	This results in structures similar to the higher cutoff at the cost of the default cutoff. We reiterate that {{TAG\|PSTRESS}} should only be used if the higher cutoff is not a viable option, as this only improves the structure and not the energy.		This results in structures similar to the higher cutoff at the cost of the default cutoff. We reiterate that {{TAG\|PSTRESS}} should only be used if the higher cutoff is not a viable option, as this only improves the structure and not the energy.