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Subsections
4.20 FFPT  A Finite Field Perturbation Program
Many molecular properties of wave functions can be computed using the
FFPT program module in MOLCAS. It adds the requested operator to
the integrals computed by the seward module. This must be done
before the MOLCAS module calculating the required wave function is requested
so the FFPT module is best run directly after the seward
module.
The TITLe keyword behaviors in a similar fashion to other
MOLCAS modules.
The sample input below contains the FFPT input
requesting that the dipole moment operator be added to the integrals
using the DIPOle keyword.
The size and direction is specified using the COMP keyword
which accepts free format input. We can compute the dipole of the
molecule by numerical determination of the gradient of the energy
curve determined for several values of the dipole operator. From the second
derivative we can obtain the polarizability component.
Sample input requesting the FFPT module to
include a dipole moment operator in the integral file:
&FFPT
Title= Finite Perturbation with a dipole in the x negative of strength 0.1 au
FFPT
Dipole
Comp
X 0.1
The ffpt section of the output is short and self
explanatory. The ONEINT file is updated with the requested
operator.
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Up: 4. Program Based Tutorials
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