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}}. | 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[math]\displaystyle{ \times 0.8 }[/math] | for ALGO=ACFDT |
| = ENCUTGW[math]\displaystyle{ \times 0.8 }[/math] | as of VASP.6.3 | |
| = ENCUTGW | else |
| Important: For vasp.6.3 and later releases ENCUTGWSOFT always defaults to ENCUTGW[math]\displaystyle{ \times 0.8 }[/math]. |
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 [math]\displaystyle{ \mathbf{G}_{\rm max } }[/math]. Thus VASP automatically extrapolates to the infinite basis set limit using a linear regression to the equation: [1][2][3]
[math]\displaystyle{ 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 ACFDT calculations and MP2 calculations. The modified Coulomb kernel is in this case: [math]\displaystyle{ 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} \gt \mathrm{ENCUTGWSOFT} }[/math]
If LSCK is set to .TRUE., the squeezed Coulomb kernel is used instead of the cosine window:[4]
[math]\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}\lt \frac{\hbar^2 G^2}{2m_e}\lt \frac{\hbar^2G_{max}^2}{2m_e}=\mathrm{ENCUTGW} }[/math]
This kernel squeezes contributions from large wave vectors [math]\displaystyle{ G\gt G_{max} }[/math] 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