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##

MP2 calculations

Available only in VASP.5.X. MP2 is currently experimental,
documentation under construction and for internal use only!

Specifying `ALGO`=MP2 VASP calculates MP2 correlation energies.
It is strongly recommended to calculate *all* virtual states spanned
by the basis set before calling the MP2 routines.

Thus any MP2 calculation should proceed in three steps. The first step
is the determination of the occupied orbitals of the Hartree-Fock Hamiltonian:

LHFCALC = .TRUE.
AEXX = 1.0 ; ALDAC = 0.0 ; AGGAC = 0.0
ALGO = D ; EDIFF = 1E-7

Note that MP2 requires to calculate the Hartree-Fock groundstate, and any
LDA or GGA correlation should be switched off.
Next search for `maximum number of plane-waves:` in the OUTCAR file and
execute VASP again using the following INCAR file:
NBANDS = maximum number of plane-waves
LHFCALC = .TRUE.
AEXX = 1.0 ; ALDAC = 0.0 ; AGGAC = 0.0
ALGO = Exact ; NELM = 1 ; LOPTICS = .TRUE.

Finally calculate the MP2 correlation energy:
NBANDS = maximum number of plane-waves
LHFCALC = .TRUE. ; AEXX = 1.0 ; ALDAC = 0.0
LMAXMP2 = 2

The flag LMAXMP2 specifies the maximum quantum number for
the treatment of the one-center terms. This should be set to
twice the maximum non local component in the pseudopotential
(see also 6.71.6 and 6.71.7.
Alternatively `LMAXFOCKAE` can be set in the INCAR file. This
is expected to be more efficient, but slightly less accurate. Combining
`LMAXFOCKAE` and `LMAXFOCKMP2` is also in principle allowed
but hardly offers any advantage over using only `LMAXFOCKAE`
or `LMAXFOCKMP2`.

N.B. Requests for support are to be addressed to: vasp.materialphysik@univie.ac.at