MOLPRO uses two 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 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. The present version 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, DFT, MCSCF, MP2, LMP2, and QCISD. It does not work with state averaged SA-MCSCF wave functions.
The Alaska gradients are default for general contracted basis sets. In all other cases the Cadpac gradients are default. On most architectures these are faster than Alaska gradients. However, it is possible to choose the gradients 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 30.2.22). Note that for computing gradients for state-averaged MCSCF a CPMCSCF is required in the MCSCF calculation (see CPMCSCF).
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.
P.J. Knowles and H.-J. Werner