4.3 Method and wavefunction specification

After defining the geometry and basis set (in any order) one has to specify
the methods to be used. This is simply done by keywords, which are normally
the same as the usual abbreviations for the methods (`HF` for Hartree-Fock, `MP2` for
second-order Møller-Plesset perturbation theory, or `CCSD(T)` for coupled-cluster with
singles and doubles and perturbative triples.
In most cases, the first step is a Hartree-Fock calculation, in which the
molecular orbitals to be used in subsequent electron correlation treatments
are optimized. An arbitary number of different methods can be executed
after each other, just by giving the corresponding keywords. For example

geometry={...} basis=... hf !orbital optimization using HF mp2 !MP2 calculation using the HF orbitals mp4 !MP4 calculation using the HF orbitals ccsd(t) !CCSD(T) calculation using the HF orbitals

Note, howeverm that MP2 is part of MP4 and CCSD, and therefore the mp2 calculation in the above input is redundant.

molpro@molpro.net 2018-11-14