star(MVOCAL)

Introduction

Modified virtual orbitals.

The virtual canonical Hartree-Fock orbitals are not the optimal choice for correlated calculations in which the virtual space is truncated; the lower orbitals tend to be diffuse since they see the N + 1 electron system. One may exploit the freedom of rotation amongst the virtual orbitals to obtain orbitals better suited for correlated calculations. The default option in DIRAC when WAVE_FUNCTION_.MVO has been specified is to generate the modified virtual orbitals by construction of a Fock operator for the system with some electrons removed, as first proposed by Bauschlicher [Bauschlicher1980]. The orbital string specified with MVOCAL_.VECMVO specifies which occupied orbitals to include in the construction of the modified Hartree-Fock potential for the virtual orbitals.

Note that the resulting modified virtual orbitals are no longer canonical and can not be used in MP2 calculations; they can be used in the various CI and CC modules, and as start orbitals for *KRMCSCF.

Keywords

keyword(PRINT)

Print level.

Default:

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keyword(VECMVO)

Read Specification of orbital strings of orbitals to be included in the Hartree-Fock potential when constructing the cationic Fock operator. Default is the doubly-occupied molecular orbitals from the SCF.

keyword(INTFLG)

Specify what two-electron integrals to include during the construction of the modified virtual orbitals (default: HAMILTONIAN_.INTFLG under **HAMILTONIAN).