LSCK

LSCK = [logical]
Default: LSCK = .FALSE.

Description: LSCK=True switches on the use of the squeezed Coulomb kernel.

If LSCK is set to .TRUE., the squeezed Coulomb kernel is used instead of the cosine window ^[1]:

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

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