18 CASSCF Geometry Optimisations

We consider below a CASSCF calculation on the X¹A₁ state of H₂O, using a full valence criterion in specifying the active space so that the formally vacant SCF virtual MOs, 4a₁ and 2b₂, are permitted variable occupancy. This example utilises the vectors from the closed shell SCF calculation of Example 1.

          #!/bin/csh -f
          cd /scr1/user    
          setenv ed2 h2omain
          setenv ed3 h2odump
          /scr1/wab/GAMESS-UK/bin/gamess << EOF
          restart new
          title
          water  at casscf level 3-21g basis set
          zmat angstrom
          o
          h 1 oh
          h 1 oh 2 hoh
          variables
          oh 0.956
          hoh 104.5
          end
          scftype casscf
          config print
          doc 1 to 5
          uoc 6 7
          end
          superci 1 to 8
          newton 9 to 20
          hessian 9 to 20
          simul 9 to 20
          enter
          EOF

The following points should be noted:

• It is not possible to use BYPASS in the above, given the data for the SCF job of Example 1. This would have resulted in generation of a P-supermatrix which is not usable in a CASSCF run (see Part 2, Table 1).
• CASSCF calculations require two scratch FORTRAN data sets, FT01 and FT02.

In the above we have assumed that the CASSCF calculation completes in the time allocated, with the associated direct-access files allocated in default scratch status. The following job is typical of that required if restarts of the CASSCF step are envisaged:

          #!/bin/csh -f
          cd /scr1/user
          setenv ed1 h2oed1
          setenv ed2 h2omain
          setenv ed3 h2odump
          setenv ed4 h2oed4
          setenv ed6 h2oed6
          setenv ed9 h2oed9
          setenv ed10 h2oed10
          /scr1/wab/GAMESS-UK/bin/gamess << EOF
          restart new
          title
          water at casscf level 3-21g basis set
          zmat angstrom
          o
          h 1 oh
          h 1 oh 2 hoh
          variables
          oh 0.956
          hoh 104.5
          end
          scftype casscf
          config print
          doc 1 to 5
          uoc 6 7
          end
          superci 1 to 8
          newton 9 to 20
          hessian 9 to 20
          simul 9 to 20
          enter
          EOF

Assuming the above job terminated prior to convergence, the calculation might be restarted as follows:

          #!/bin/csh -f
          cd /scr1/user
          setenv ed1 h2oed1
          setenv ed2 h2omain
          setenv ed3 h2odump
          setenv ed4 h2oed4
          setenv ed6 h2oed6
          setenv ed9 h2oed9
          setenv ed10 h2oed10
          /scr1/wab/GAMESS-UK/bin/gamess << EOF
          restart scf
          title
          water at casscf level 3-21g basis set
          zmat angstrom
          o
          h 1 oh
          h 1 oh 2 hoh
          variables
          oh 0.956
          hoh 104.5
          end
          scftype casscf
          config bypass
          doc 1 to 5
          uoc 6 7
          end
          superci 1 to 2
          newton 3 to 20
          hessian 3 to 20
          simul 3 to 20
          vectors 6 7
          enter 6 7
          EOF

where the default sections housing the CASSCF vectors and ci coefficients (sections 6 and 7 respectively) created in the startup job are explicitly declared above, and CONFIG processing is bypass'ed. Having completed the single point calculation, the following might be used to perform a geometry optimisation at the CASSCF level. Note that it is now necessary to SAVE the data set associated with ED11 if restarts are envisaged.

          #!/bin/csh -f
          cd /scr1/user
          setenv ed1 h2oed1
          setenv ed2 h2omain
          setenv ed3 h2odump
          setenv ed4 h2oed4
          setenv ed6 h2oed6
          setenv ed9 h2oed9
          setenv ed10 h2oed10
          setenv ed11 h2oed11
          /scr1/wab/GAMESS-UK/bin/gamess << EOF
          restart new
          title
          water - geometry optimisation at casscf level
          zmat angstrom
          o
          h 1 oh
          h 1 oh 2 hoh
          variables
          oh 0.956
          hoh 104.5
          end
          runtype optimise
          scftype casscf
          config bypass
          doc 1 to 5
          uoc 6 7
          end
          superci 1 to 5
          newton 6 to 20
          hessian 6 to 20
          simul 6 to 20
          enter
          EOF

Again the default CASSCF vector and CI coefficient sections from the initial energy calculation will be used by default in the optimisation job.