11 Geometry optimization

Geometry optimizations are invoked by the `optg` input directive, which must follow
the input of the method for which the optimization is to be performed. For instance,
optimization of the geometry for formaldehyde at the MP2 level is performed with the
following input

***,formaldehyde print,basis,orbitals !this is optional: print the basis set and the !occupied orbitals angstrom geometry={ !define the nuclear coordinates C O , C , rco H1 , C , rch , O , hco H2 , C , rch , O , hco , H1 , 180 } rco=1.182 Ang rch=1.102 Ang hco=122.1789 Degree basis=vdz !Select basis set hf !Perform HF calculation mp2 !Perform MP2 calculation optg !Optimize geometry for MP2

Optimizations use analytical energy gradients if available; otherwise the gradients are computed by finite differences. Presently, analytical energy gradients are available for the following methods.

`hf`- Closed and open-shell spin restricted Hartree-Fock (RHF)
`uhf`- Spin-unrestricted Hartree-Fock (UHF).
`ks`- Spin-restricted closed and open-shell Kohn-Sham calculations.
`uks`- Spin-unrestricted Kohn-Sham calculations.
`mcscf`- MCSCF and CASSCF, including state-averaged calculations
`mp2`- closed-shell MP2
`df-mp2`- closed-shell MP2 with density fitting
`lmp2`- closed-shell local MP2
`df-lmp2`- closed-shell local MP2
`ccsd`- closed-shell quadratic configuration
`ccsd`- closed-shell asingles and doubles coupled-cluster
`qcisd(t)`- closed-shell quadratic configuration, including triples interaction, including perturbative triple-excitation contribution
`rs2`- Second-order multireference perturbation theory, including multi-state treatments

Various options are available for modifying the convergence thresholds and the optimization method. For details see the reference manual.

molpro@molpro.net 2019-03-21