Exchange-correlation functional parameters
The parameters here are used in various exchange-correlation (XC) functionals. In nanodcal, XC functional calculation is done by plug-in calculators. Several XC functionals can be chosen by the user. On the other hand, the users can input their own XC functionals by plug-in their calculators to nanodcal.
calculation.xcFunctional.Type
keyword: calculation.xcFunctional.Type
possible values: ‘LDA_PZ81’, ‘LDA_VWN80’, ‘LDA_PW92’, ‘GGA_PBE96’, ‘GGA_REVPBE98’, ‘GGA_RPBE99’, ‘mixed’
default value: ‘LDA_PZ81’
description: The type of exchange-correlation functional to be used. While ‘LDA_PZ81’, ‘LDA_VWN80’, ‘LDA_PW92’, ‘GGA_PBE96’, ‘GGA_REVPBE98’, and ‘GGA_RPBE99’ are well-known functionals, the option ‘mixed’ is for users to mix different types of exchange and/or correlation functionals.
If calculation.xcFunctional.calculator is given, this parameter will not be used.
an example:
calculation.xcFunctional.Type = 'LDA_PZ81'
'GGA_REVPBE98', 'GGA_RPBE99', 'mixed'
calculation.xcFunctional.Weight
keyword: calculation.xcFunctional.Weight
possible values: 2 x 2 cell array when a well-known exchange and correlation functional is used; n X 2 cell array, with n a integer, when the mixed type of exchange and correlation functional is used.
default value: {‘X’,1.0;’C’,1.0} for regular type; no default value for mixed type.
description: When a well-known exchange and correlation functional is used, it gives weights for the exchange energy and the correlation energy. When mixed type is used, it specifies the exchange and/or correlation functionals to be mixed and the corresponding mixing weights. All exchange and correlation functionals which may be used in the mixing is listed as follows with a short
description: xLDA — LDA exchange cPZ81 — PZ correlation (Phys. Rev. B 23, 5048) cVWN80 — VWN correlation (Can. J. Phys. 58, 1200) cPW92 — PW92 correlation (Phys. Rev. B 45, 13244) xPBE96 — PBE exchange (Phys. Rev. Lett. 77, 3865) xREVPBE98 — REVPBE exchange (Phys. Rev. Lett. 80, 890) xRPBE99 — RPBE exchange (Phys. Rev. B 59, 7413) xEV93 — EV exchange (Phys. Rev. B 47, 13164) cPBE96 — PBE correlation (Phys. Rev. Lett. 77, 3865)
If calculation.xcFunctional.calculator is given, this parameter will not be used.
an example:
(for regular type)
calculation.xcFunctional.Weight = {'X',1.0;'C',1.0}
another example: (for mixed type):
calculation.xcFunctional.Weight = ...
{'xLDA',0.2;'cVWN80',1.0;'xPBE96',0.8}
calculation.realEcontour.etaSigma
keyword: calculation.realEcontour.etaSigma
possible values: a small double number
default value: 1e-6 Hartree
description: the small eta used in the calculation of self-energy along the real energy contour. In analytical Greens function theory, the eta is a positive infinitesimal.
an example:
calculation.realEcontour.etaSigma = 1e-4
calculation.realEcontour.etaGF
keyword: calculation.realEcontour.etaGF
possible values: a small double number
default value: 1e-6 Hartree
description: the small eta used in the calculation of Greens function along the real energy contour. In analytical Greens function theory, this is a positive infinitesimal.
an example:
calculation.realEcontour.etaGF = 1e-4
calculation.realEcontour.eta
keyword: calculation.realEcontour.eta
possible values: a small double number
default value: 5e-4, 2e-5, or 1e-6 Hartree, depending on the value of the parameter calculation.control.precision.
description: the small eta used in the calculation of self-energy and/or Greens function along the real energy contour. This parameter is not used when the parameter realEcontour.etaSigma and/or realEcontour.etaGF is given.
an example:
calculation.realEcontour.eta = 1e-4