Posted by Roland Lindh on September 26, 2005 at 20:57:02:
In Reply to: Offdiagonal Dipole Moment Matrix Element. posted by Chaehyuk Ko on September 25, 2005 at 21:29:51:
Hi,
the CASPT2 method is not a variational method, hence properties can not be computed as expectation values as a simple trace of the density matrix with the property integrals. One common way to get around this problem is to use a so-called finite field technique. In this one apply a small electric field to the molecule and register the change of the energy. The energy is Taylor expaned with respect to the electric field. The first derivative in this series is the dipole moment. Do as follows: apply a small electric field, both plus and minus, along each of the cartesian direction (note that if your molecule is symmetric along one direction that you have to remove this symmetry, better and simpler remove any explicit symmetry specification). Compute the dipole moment numerically from
mu_x = (E(deltaF_x) - E(-deltaF_x))/(2*deltaF_x)
Look at the manual for the FFPT module for further instructions.
Take care,
-roland
-roland