45.1 Analytical energy gradients

MOLPRO uses different gradient programs:

The CADPAC gradient program is based on the CADPAC integral routines by R. D. Amos. Currently, this program works for closed shell SCF, high spin RHF, and (state averaged) MCSCF. In the MCSCF case the wavefunction must either be fully optimized, or frozen core orbitals must be taken from a closed-shell SCF calculation (but this does not work in the case of state-averaged MCSCF). Note that CADPAC does not work with generally contracted basis functions.

The ALASKA gradient program is based on the SEWARD integral routines by R. Lindh. It allows the calculation of gradients of generally contracted basis functions for closed shell SCF, open shell RHF, UHF, RKS, UKS, MCSCF, MP2, LMP2, DF-LMP2, QCISD, QCISD(T), CCSD, DCSD and RS2 (CASPT2). Gradients for state averaged MCSCF wave functions can be evaluated using the RS2 gradient program, see section 45.1.5. For details about CASPT2 gradients, see section 21.7.

The AIC density fitting integral program written by G. Knizia computes two- and three-index integrals and integral derivatives. This program is used for computing gradients for the DF-MP2, DF-LMP2, state averaged DF-MCSCF, and DF-CASPT2 methods.

By default, the program uses ALASKA gradients whenever possible.
However, it is possible to force the use of a particular gradient program by defining
the variable `GRADTYP` before calling the gradient program:

The gradient program is called using the `FORCE` command:

Normally, the `FORCE` command is not needed, since geometry optimizations
should be performed using the `OPTG` procedure. An exception is the optimization
of counterpoise corrected energies, which requires several force calculations (cf. section 46.4.7).

If no further data cards are given, the
default is to evaluate the gradient for the last optimized wavefunction.
In this case no further input is needed for ordinary gradient cases
(the program remembers the records on which the wavefunction information
is stored). An exception is the unusual case that several different `CPMCSCF`
calculations have been formed in a previous MCSCF calculation. In this case
the `SAMC` directive must be used to select the desired record.
If analytical gradients are not available for the last wavefunction, the gradient
is computed numerically. For more details regarding numerical energy gradients see section 45.2.

- 45.1.1 Adding gradients (
`ADD`) - 45.1.2 Scaling gradients (
`SCALE`) - 45.1.3 Defining the orbitals for SCF gradients (
`ORBITAL`) - 45.1.4 MCSCF gradients (
`MCSCF`) - 45.1.5 State-averaged MCSCF gradients with SEWARD
- 45.1.6 State-averaged MCSCF gradients with CADPAC
- 45.1.7 Non-adiabatic coupling matrix elements (
`NACM`) - 45.1.8 Difference gradients for SA-MCSCF (
`DEMC`) - 45.1.9 Example