DFT-ulg

In the DFT-ulg method of Kim et al., the correction term takes the form:

[math]\displaystyle{ E_{\mathrm{disp}} = -\frac{1}{2} s_{lg}\sum_{i=1}^{N_{at}} \sum_{j=1}^{N_{at}} \sum_{\mathbf{L}} {}^{\prime} \frac{C_{6ij}}{r_{ij,L}^{6}+b_{lg}(R_{0}^{ij})^{6}} }[/math]

where the first two summations are over all [math]\displaystyle{ N_{at} }[/math] atoms in the unit cell and the third summation is over all translations of the unit cell [math]\displaystyle{ {\mathbf{L}}=(l_1,l_2,l_3) }[/math] where the prime indicates that [math]\displaystyle{ i\not=j }[/math] for [math]\displaystyle{ {\mathbf{L}}=0 }[/math]. [math]\displaystyle{ C_{6ij} }[/math] denotes the dispersion coefficient for the atom pair [math]\displaystyle{ ij }[/math], [math]\displaystyle{ {r}_{ij,\mathbf{L}} }[/math] is the distance between atom [math]\displaystyle{ i }[/math] located in the reference cell [math]\displaystyle{ \mathbf{L}=0 }[/math] and atom [math]\displaystyle{ j }[/math] in the cell [math]\displaystyle{ L }[/math].

Usage

The DFT-ulg method can be activated by setting IVDW=3. The parameters in the DFT-ulg method (see Ref. for details) that can be modified are listed below.

• VDW_RADIUS=50.0 : cutoff radius (in [math]\displaystyle{ \AA }[/math]) for pair interactions
• VDW_S6=0.7012 : global scaling parameter [math]\displaystyle{ s_{lg} }[/math]
• VDW_D=0.6966 : universal correction parameter [math]\displaystyle{ b_{lg} }[/math]
• VDW_C6=[real array] : [math]\displaystyle{ C_6 }[/math] parameters ([math]\displaystyle{ \mathrm{Jnm}^{6}\mathrm{mol}^{-1} }[/math]) for each species defined in the POSCAR file
• VDW_R0=[real array] : [math]\displaystyle{ R_0 }[/math] parameters ([math]\displaystyle{ \AA }[/math]) for each species defined in the POSCAR file
• LVDW_EWALD=.FALSE. : the lattice summation in [math]\displaystyle{ E_{\mathrm{disp}} }[/math] expression is computed by means of Ewald's summation (.TRUE. ) or via a real space summation over all atomic pairs within cutoff radius VDW_RADIUS (.FALSE.). (available in VASP.5.3.5 and later)

Mind: The default value of the parameter [math]\displaystyle{ s_{lg} }[/math] (0.7012) was determined in conjunction with the PBE GGA functional. Therefore, it is not recommended to use the DFT-ulg dispersion correction with a GGA functional other than PBE, unless [math]\displaystyle{ s_{lg} }[/math] is reoptimized.

Related tags and articles

VDW_RADIUS, VDW_S6, VDW_D, VDW_C6, VDW_R0, LVDW_EWALD, IVDW, DFT-D2

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