ENCUTGWSOFT

ENCUTGWSOFT = [real] 

Default: ENCUTGWSOFT	= ENCUTGW$\times 0.8$	for ALGO=ACFDT
	= ENCUTGW$\times 0.8$	as of VASP.6.3
	= ENCUTGW	else

Important: For vasp.6.3 and later releases ENCUTGWSOFT always defaults to ENCUTGW$\times 0.8$.

Descprition: The flag ENCUTGWSOFT sets the energy cutoff for response function, such that it allows to truncate the Coulomb kernel slowly between the energy specified by ENCUTGWSOFT and ENCUTGW using a cosine window function.

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This usually leads to much smoother energy-volume curves in ACFDT calculations and MP2 calculations. The modified Coulomb kernel is in this case: $v_{G}={\frac {4\pi e^{2}}{G^{2}}}{\frac {1}{2}}\left(1+\cos \left(\pi \,{\frac {{\frac {\hbar ^{2}G^{2}}{2m_{e}}}-\mathrm {ENCUTGWSOFT} }{\mathrm {ENCUTGW} -\mathrm {ENCUTGWSOFT} }}\right)\right)\qquad {\mbox{for}}\quad {\frac {\hbar ^{2}G^{2}}{2m_{e}}}>\mathrm {ENCUTGWSOFT}$

If LSCK is set to .TRUE., the squeezed Coulomb kernel is used instead of the cosine window:

$v_{G}=4\pi e^{2}{\frac {(G_{max}-G_{min})(G_{max}-G)}{(G_{min}^{2}-G(2G_{min}-G_{max}))^{2}}}\qquad {\mbox{for}}\quad \mathrm {ENCUTGWSOFT} ={\frac {\hbar ^{2}G_{min}^{2}}{2m_{e}}}<{\frac {\hbar ^{2}G^{2}}{2m_{e}}}<{\frac {\hbar ^{2}G_{max}^{2}}{2m_{e}}}=\mathrm {ENCUTGW}$

This kernel squeezes contributions from large wave vectors $G>G_{max}$ into the window given by ENCUTGWSOFT. Effectively, this extrapolates the RPA correlation energy to the ENCUTGW $\to \infty$ limit, assuming that the basis set incompleteness error falls off as $1/\mathrm {ENCUTGW} ^{3/2}$.

Related tags and articles

PRECFOCK, ENCUT, ENCUTGW, GW calculations, LSCK RPA/ACFDT basis set convergence Examples that use this tag

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