MOLPRO

23 MØLLER PLESSET PERTURBATION THEORY 179
The commands MP2, MP3, MP4 perform the MP calculations up to the specified order (lower
orders are included).
MP4;NOTRIPL; performs MP4(SDQ) calculations.
Normally, no further input is needed if the MPn card directly follows the corresponding HF-
SCF. Otherwise, occupancies and orbitals can be specified as in the CI program. The resulting
energies are stored in variables as explained in section 8.8.
Dual basis set calculations are possible for the closed-shell methods, see section 24.9.
23.1 Expectation values for MP2
One-electron properties can be computed as analytical energy derivatives for MP2. This calculation
is much more expensive than a simple MP2, and therefore only done if an EXPEC
card follows the MP2 card (the GEXPEC directive has no effect in this case). The syntax of the
EXPEC card is explained in section 6.13. For an example, see section 24.6.1.
The density matrix can be saved using
{MP2;DM[,record.ifil]}
See also sections 24.7 and 24.8.
For changing the accuracy and other parameters of the CPHF calculation see section 23.3.
23.2 Polarizabilities and second-order properties for MP2
Analytical MP2 static dipole polarizabilities and other second order propeties can be computed
using the POLARI. By default the dipole operator is used, but other one-electron operators
can be specified on the POLARI directive. Currently, this is only working without frozen core
orbitals, i.e., ⁀ CORE,0 must be given. The dipole polarizabilities are stored in the variables
POLXX, POLXY, POLXZ, POLYY, POLYZ, POLZZ.
Example:
{ mp2
core,0
polari,dm,qm}
Computes the full tensors for the dipole and quadrupole operators.
23.3 CPHF for gradients, expectation values and polarizabilities
The accuracy and other parameters of the CPHF calculations necessary to compute gradients
and response properties can be modified using the CPHF directive:
CPHF, [THRMIN=thrmin], [THRMAX=thrmax], [MAXIT=maxit], [SHIFT=shift], [SAVE=record],
[START=record], [DIIS=idiis], [DISM=idism]
THRMIN
CPHF convergence threshold (default 1.d-6). THRESH and ACCU are
aliases for this.