MOLPRO

41 ENERGY GRADIENTS 301
41.1.9 Example
***, Calculate Gradients for Water
alpha=104 degree
!set geometry parameters
r=1 ang
geometry={O;
!define z-matrix
H1,o,r;
H2,o,r,H1,alpha}
basis=vdz
!basis set
hf
!do scf
forces
!compute gradient for SCF
mp2
!mp2 calculation
forces
!mp2 gradients
multi
!casscf calculation
forces
!casscf gradient
http://www.molpro.net/info/current/examples/h2o_forces.com
41.2 Numerical gradients
It is possible to compute gradients by finite differences using
FORCE,NUMERICAL,options
Numerical gradients are computed automatically if no analytical gradients are available for the
last energy calculation. By default, no further input are needed, and the gradient will be computed
for the last energy calculation. The following options can be given on the FORCE command
or on subsequent directives (see subsequent sections):
STARTCMD=command
PROC=procname
VARIABLE=varname
The input between command and the current FORCE command defines
the energy calculation for which the gradient is computed. This
input section is executed for each displacement.
specifies a procedure to be executed for each displacement. This must
define a complete energy calculation and must not contain gradient or
Hessian calculations.
Compute the gradient of the value of variable varname. This implies
numerical gradients. The variable must be set in the corresponding
energy calculation.
COORD=ZMAT|CART|3N coordinates with respect to which the gradient is evaluated. See
section 41.2.1 for more information.
DISPLACE=ZMAT|SYM|UNIQUE|CART
Displacement coordinates to be used for numerical gradient. The default
is ZMAT if the geometry is given as a zmatrix which depends
on variables, and SYM (symmetrical displacement coordinates) otherwise.
See section 41.2.1 for more information.
SYMMETRY=AUTO|NOSYM Symmetry to be used in wavefunction calculations of numerical
gradients. This option is only relevant if DISPLACE=UNIQUE|CART.
If AUTO is given, the maximum possible symmetry is used for each
displacement. This implies that the energy is independent of the symmetry
used. Note that this often not the case in MRCI or CASPT2
calculations. The option can also not be used in local correlation calculations.
AUTO
(logical). Same as SYMMETRY=AUTO