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 HF 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 = S ; 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 $l$ 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 6.64.5 and 6.64.6. Note that alternatively LMAXFOCKAE can be set in the INCAR file, but this is exepected to be slightly less accurate, and combining LMAXFOCKAE and LMAXFOCKMP2 is also allowed (this, however, makes hardly a lot of sense).