.. _functionals:

Exchange-correlation functionals
================================

The following functionals are implemented within XCFun

   ===========    ========
   SLATERX        Slater LDA exchange
   PW86X          PW86 exchange
   VWN5C          VWN5 LDA Correlation functional
   PBEC           PBE correlation functional
   PBEX           PBE Exchange Functional
   BECKEX         Becke 88 exchange
   BECKECORRX     Becke 88 exchange correction
   BECKESRX       Short range Becke 88 exchange
   LDAERFX        Short-range spin-dependent LDA 
                  exchange functional
   LDAERFC        Short-range spin-dependent LDA 
                  correlation functional
   LDAERFC_JT     Short-range spin-unpolarized LDA 
                  correlation functional
   LYPC           LYP correlation
   OPTX           OPTX Handy & Cohen exchange
   REVPBEX        Revised PBE Exchange Functional
   RPBEX          RPBE Exchange Functional
   SPBEC          sPBE correlation functional
   VWN_PBEC       PBE correlation functional using VWN LDA 
                  correlation.
   KTX            KT exchange GGA correction
   TFK            Thomas-Fermi Kinetic Energy Functional
   PW91X          Perdew-Wang 1991 GGA Exchange Functional
   PW91K          PW91 GGA Kinetic Energy Functional
   PW92C          PW92 LDA correlation
   M05X           M05 exchange
   M05X2X         M05-2X exchange
   M06X           M06 exchange
   M06X2X         M06-2X exchange
   M06LX          M06-L exchange
   M06HFX         M06-HF exchange
   M05X2C         M05-2X Correlation
   M05C           M05 Correlation
   M06C           M06 Correlation
   M06LC          M06-L Correlation
   M06X2C         M06-2X Correlation
   TPSSC          TPSS original correlation functional
   TPSSX          TPSS original exchange functional
   REVTPSSC       Revised TPSS correlation functional
   REVTPSSX       Reviewed TPSS exchange functional
   PZ81C          PZ81 LDA correlation
   P86C           P86C GGA correlation
   RANGESEP_MU    Range separation inverse length [1/a0]
   EXX            Amount of exact (HF like) exchange 
                  (must be provided externally)
   ===========    ========


Implementing a new XC functional
--------------------------------

.. warning:: To be written

Introducing new variables
-------------------------

.. warning:: To be written
