MOLPRO

41 ENERGY GRADIENTS 298
41 ENERGY GRADIENTS
41.1 Analytical energy gradients
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 (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), and RS2
(CASPT2). Gradients for state averaged MCSCF wave functions can be evaluated using the RS2
gradient program, see section 41.1.5. For details about CASPT2 gradients, see section 21.7.
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:
GRADTYP=ALASKA
GRADTYP=CADPAC
The gradient program is called using the FORCE command:
FORCE
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 42.4.7).
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 MC-
SCF 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 41.2.
41.1.1 Adding gradients (ADD)
ADD,factor,[NOCHECK];
If this card is present, the current gradient and energy are added to the previous ones using the
given factor. This is useful for the optimization of counterpoise corrected energies (cf. 42.4.7).
By default, the program will stop with an error message unless NOORIENT has been specified
in the geometry input. This behaviour can be disabled by the NOCHECK option. This option
should only be given if all gradients which are added are evaluated at exactly the same nuclear
geometry; otherwise wrong results could result due to unintended rotations of the system.
41.1.2 Scaling gradients (SCALE)
SCALE,factor;