The MBPT2 program computes second-order Many Body Perturbation Theory calculations based on a RHF-type of wave function (MP2 method). The calculation is to some extent defined by the SCF calculation which must be performed before running the MBPT2 program. Therefore, there is no difficulty related to the input file unless an analysis of the correlation energies of specific electron pairs or contribution from external orbitals wants to be performed. In this case keywords SFROzen and SDELeted have to be used as described in section mbpt2 (in users guide) of the user's guide.
To run the program the ONEINT and ORDINT integral files generated by the SEWARD program and the COMFILE file generated by the SCF program are needed. The program can be otherwise run in a direct manner. Therefore the SEWARD program must be run with the option ONEOnly included in its input. Only the ONEINT will be then generated and used by the SCF and MBPT2 modules. The input file used to run a MBPT2 calculation on the ground state of the water molecule is displayed in figure 3.14.
Figure 3.14. Sample input requested by the mbpt2 module to
calculate the MP2 energy for the ground state of the water in C
symmetry.
&MBPT2 &END Title MP2 of ground state of C2v Water Frozen 1 0 0 0 End of Input
The output of MBPT2 is self-explanatory.