The library provides a collection of built-in functionals, coded by J.M. Soler and C. Balbás, and an interface to the LibXC library for a wider selection of semi-local (LDA and GGA) functionals. Support for the MGGA functionals in LibXC is being implemented.
The built-in functionals are classified by family (LDA (or LSD), GGA, VDW) and authors:
'CA' or 'PZ' => LSD Perdew & Zunger, PRB 23, 5075 (1981)
'PW92' => LSD Perdew & Wang, PRB, 45, 13244 (1992)
'PW91' => GGA Perdew & Wang, JCP, 100, 1290 (1994)
'PBE' => GGA Perdew, Burke & Ernzerhof, PRL 77, 3865 (1996)
'RPBE' => GGA Hammer, Hansen & Norskov, PRB 59, 7413 (1999)
'revPBE' => GGA Zhang & Yang, PRL 80,890(1998)
'LYP' => GGA Becke-Lee-Yang-Parr (see subroutine blypxc)
'WC' => GGA Wu-Cohen (see subroutine wcxc)
'PBESOL' => GGA Perdew et al, PRL, 100, 136406 (2008)
'AM05' => GGA Mattsson & Armiento, PRB, 79, 155101 (2009)
'PBEJsJrLO' => GGA Reparametrizations of the PBE functional by
'PBEJsJrHEG' => GGA L.S.Pedroza et al, PRB 79, 201106 (2009) and
'PBEGcGxLO' => GGA M.M.Odashima et al, JCTC 5, 798 (2009)
'PBEGcGxHEG' => GGA using 4 different combinations of criteria
These are the semi-local components used in some exact-exchange calculations:
'HSE6' => (Heyd–Scuseria–Ernzerhof) J. of Chemical Physics 120, 16 (2004)
'PBE0' => J. Chem. Phys. 110, 6158 (1999)
https://doi.org/10.1063/1.478522
'DRSLL' => VDW Dion et al, PRL 92, 246401 (2004)
'LMKLL' => VDW K.Lee et al, PRB 82, 081101 (2010)
'KBM' => VDW optB88-vdW of J.Klimes et al, JPCM 22, 022201 (2010)
'C09' => VDW V.R. Cooper, PRB 81, 161104 (2010)
'BH' => VDW K. Berland and Per Hyldgaard, PRB 89, 035412 (2014)
'VV' => VDW Vydrov-VanVoorhis, JCP 133, 244103 (2010)
To access these functionals, one can simply call the setXC_family_authors routine:
call setxc_family_authors('GGA', 'PBE')
The library offers also an expanded version of this routine that is able to describe cocktail mixings of functionals, each with its appropriate weight. For example,
call setXC( 2, (/'GGA','GGA'/), (/'PBE','WC'/), (/1.0_dp, 0.0_dp/), (/0.75_dp,0.25_dp/) )
will use a cocktail of PBE and WC in which the exchange part is 100% PBE, and the correlation part is 75% PBE and 25% WC.
In LibXC, most functionals are split by exchange and correlation parts. For example, there are separate functionals for the exchange and corrrelation parts of PBE, respectively XC_GGA_X_PBE (id 101) and XC_GGA_C_PBE (id 130). The id or functional number, while not human friendly, is the recommended way of identification for full compatibility.
To tell libGridXC that a PBE functional from LibXC is desired, we can use the call:
call setXC_libxc_ids ( 2, (/ 101, 130 /) )
Note that this combination of exchange and correlation parts can be seen as a special kind of cocktail mixing. Hence the same result could be obtained by the call:
call setXC( 2, (/'GGA','GGA'/), (/'LIBXC-101','LIBXC-130'/), (/1.0_dp, 0.0_dp/), (/0.0_dp,1.0_dp/) )
where the "author" field is a special string of the form
LIBXC-XXXX-SYMBOL where -SYMBOL is optional if XXXX is a valid
libXC functional id. Accepted symbols are those for which the
functional_get_number routines of LibXC return a valid functional
id, and are of the form FAMILY_TYPE_NAME (for example, GGA_X_PBE
-- see the complete list in the xc_funcs.h file generated at the
time of compilation of libXC, noting that the initial XC_ has to be
removed). If the LibXC id is not known, it can be set to 0 and leave
the specification to the symbolic part. For example, the following
forms are equivalent:
LIBXC-101
LIBXC-0101
LIBXC-0-GGA_X_PBE
LIBXC-101-GGA_X_PBE
This form is more cumbersome, but it can be generalized if desired to extra mixings (even with non-libxc functionals).
A handful of LibXC functionals are "exchange-correlation". For them, the specification can simply be, for example (XC_LDA_XC_TETER93 functional, id=20):
call setXC_libxc_ids ( 1, (/ 20 /) )