Hybrid Functionals. A number of hybrid functionals, which include a mixture of Hartree-Fock exchange with DFT exchange-correlation, are available via keywords:
Becke Three Parameter Hybrid Functionals. These functionals have the form devised by Becke in 1993 [Becke93a]:
where A, B, and C are the constants determined by Becke via fitting to the G1 molecule set.
There are several variations of this hybrid functional. B3LYP uses the non-local correlation provided by the LYP expression, and VWN functional III for local correlation (not functional V). Note that since LYP includes both local and non-local terms, the correlation functional used is actually:
C*EC[LYP]+(1-C)*EC[VWN]
In other words, VWN is used to provide the excess local correlation required, since LYP contains a local term essentially equivalent to VWN.
B3P86 specifies the same functional with the non-local correlation provided by Perdew 86, and B3PW91 specifies this functional with the non-local correlation provided by Perdew/Wang 91.作者Author: sobereva 时间: 2016-3-23 23:55
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