DFT-ulg

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

$E_{\mathrm {disp} }=-{\frac {1}{2}}s_{lg}\sum _{i=1}^{N_{at}}\sum _{j=1}^{N_{at}}\sum _{\mathbf {L} }{}^{\prime }{\frac {C_{6ij}}{r_{ij,L}^{6}+b_{lg}(R_{0}^{ij})^{6}}}$

where the first two summations are over all $N_{at}$ atoms in the unit cell and the third summation is over all translations of the unit cell ${\mathbf {L} }=(l_{1},l_{2},l_{3})$ where the prime indicates that $i\not =j$ for ${\mathbf {L} }=0$. $C_{6ij}$ denotes the dispersion coefficient for the atom pair $ij$, ${r}_{ij,\mathbf {L} }$ is the distance between atom $i$ located in the reference cell $\mathbf {L} =0$ and atom $j$ in the cell $L$. 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 $\mathrm {\AA}$) for pair interactions
• VDW_S6=0.7012 : global scaling parameter $s_{lg}$
• VDW_D=0.6966 : universal correction parameter $b_{lg}$
• VDW_C6=[real array] : $C_{6}$ parameters ($\mathrm {Jnm} ^{6}\mathrm {mol} ^{-1}$) for each species defined in the POSCAR file
• VDW_R0=[real array] : $R_{0}$ parameters ($\mathrm {\AA}$) for each species defined in the POSCAR file
• LVDW_EWALD=.FALSE. : the lattice summation in $E_{\mathrm {disp} }$ 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 $s_{lg}$ (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 $s_{lg}$ 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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