ENCUTGWSOFT: Difference between revisions

Revision as of 12:37, 23 November 2021

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.

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:^[1]

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

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 Sections

PRECFOCK, ENCUT, ENCUTGW, GW calculations, LSCK

Examples that use this tag

Contents

↑ S. Riemelmoser, M. Kaltak, and G. Kresse, JCP 152(13), 134103 (2020).

[riemelmoser:jcp:2020-1] S. Riemelmoser, M. Kaltak, and G. Kresse, JCP 152(13), 134103 (2020).

[1]

@@ Line 7: / Line 7: @@
 This  usually leads to much smoother energy-volume curves in {{TAG|ACFDT calculations}} and {{TAG|MP2 calculations}}.
 The modified Coulomb kernel is in this case:
-<math>v_{\bold{G}} = \frac{4 \pi e^2} {G^2} \frac{1}{2} \left( 1 + \cos \left( \pi \, \frac{ \frac{\hbar^{2} G^2 }{2 m_e} - \mathrm{ ENCUTGWSOFT} }{ \mathrm{ENCUTGW} -  \mathrm{ENCUTGWSOFT}} \right) \right)
+<math>v_{G} = \frac{4 \pi e^2} {G^2} \frac{1}{2} \left( 1 + \cos \left( \pi \, \frac{ \frac{\hbar^{2} G^2 }{2 m_e} - \mathrm{ ENCUTGWSOFT} }{ \mathrm{ENCUTGW} -  \mathrm{ENCUTGWSOFT}} \right) \right)
 \qquad \mbox{for} \quad  \frac{\hbar^2 G^2 }{2 m_e} >  \mathrm{ENCUTGWSOFT}</math>
 If {{TAG|LSCK}} is set to .TRUE., the squeezed Coulomb kernel is used instead of the cosine window:{{cite|riemelmoser:jcp:2020}}
-<math>v_{\bold{G}} = \frac{4 \pi e^2} {| \bold{G}|^2} \frac{1}{2} \left( 1 + \cos \left( \pi \, \frac{ \frac{\hbar^{2} |\bold{G}|^2 }{2 m_e} - \mathrm{ ENCUTGWSOFT} }{ \mathrm{ENCUTGW} -  \mathrm{ENCUTGWSOFT}} \right) \right)
+<math>v_{G} = 4 \pi e^2 \frac{
-\qquad \mbox{for} \quad  G_{min}<G<G_{max} </math>
+(G_{max}-G_{min})(G_{max}-G)
+}{
+(G_{min}^2 - G(2G_{min}-G_{max}))^2
+}
+\qquad \mbox{for} \quad  \mathrm{ENCUTGWSOFT}=\frac{\hbar^2G_{min}^2}{2m_e}<\frac{\hbar^2 G^2}{2m_e}<\frac{\hbar^2G_{max}^2}{2m_e}=\mathrm{ENCUTGW}</math>
-where <math>\hbar^2 G_{max} = \mathrm{ENCUTGW}</math>
+This kernel ''squeezes'' contributions from large wave vectors <math>G>G_{max}</math> into the window given by {{TAGBL|ENCUTGWSOFT}}. Effectively, this extrapolates the RPA correlation energy to the {{TAG|ENCUTGW}} <math>\to \infty</math> limit, assuming that the basis set incompleteness error falls off as <math>1/\mathrm{ENCUTGW}^{3/2}</math>.
 == Related Tags and Sections ==
 {{TAG|PRECFOCK}},