ENCUTGWSOFT: Difference between revisions

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specified by {{TAG|ENCUTGWSOFT}} and {{TAG|ENCUTGW}} using a cosine window function.
specified by {{TAG|ENCUTGWSOFT}} and {{TAG|ENCUTGW}} using a cosine window function.
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RPA/ACFDT correlation energies converge very slowly with respect to <math>\mathbf{G}_{\rm max }</math>.
Thus VASP automatically extrapolates to the infinite basis set limit using a linear regression to the equation: {{cite|harl:2008}}{{cite|harl:2010}}{{cite|klimes:2014}}
<math>E_{\mathrm{c}}({\mathbf{G}})=E_{\mathrm{c}}(\infty)+\frac{A}{{\mathbf{G}}^3}</math>.
This  usually leads to much smoother energy-volume curves in {{TAG|ACFDT calculations}} and {{TAG|MP2 calculations}}.
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:
The modified Coulomb kernel is in this case:
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\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>  
\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>  


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>.
This kernel ''squeezes'' contributions from large wave vectors <math>G>G_{max}</math> into the window given by {{TAGBL|ENCUTGWSOFT}}.
{{NB|mind|The infinite basis set limit extrapolation for RPA/ACFDT is described in more detail [[ACFDT/RPA_calculations#Basis_set_convergence|here]].}}
== Related tags and articles ==
== Related tags and articles ==
{{TAG|PRECFOCK}},
{{TAG|PRECFOCK}},

Revision as of 14:18, 24 April 2023

ENCUTGWSOFT = [real] 

Default: ENCUTGWSOFT = ENCUTGW for ALGO=ACFDT
= ENCUTGW as of VASP.6.3
= ENCUTGW else
Important: For vasp.6.3 and later releases ENCUTGWSOFT always defaults to ENCUTGW.

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.


RPA/ACFDT correlation energies converge very slowly with respect to . Thus VASP automatically extrapolates to the infinite basis set limit using a linear regression to the equation: [1][2][3]

.

This usually leads to much smoother energy-volume curves in ACFDT calculations and MP2 calculations. The modified Coulomb kernel is in this case:

If LSCK is set to .TRUE., the squeezed Coulomb kernel is used instead of the cosine window:[4]

This kernel squeezes contributions from large wave vectors into the window given by ENCUTGWSOFT.

Mind: The infinite basis set limit extrapolation for RPA/ACFDT is described in more detail here.

Related tags and articles

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