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Rahul Singh
rahulsn@iastate.edu

          I have been doing simulations in vacuum and in water for a certain molecule. I have modeled the water using EFP and have used MP2 for the ab-intio calculations. Now, when I am comparing the energies of the molecule in water and in vacuum, the difference in energy is very large and comes around ~ 7 hartrees. This large difference has not been reported in previous papers but of course nobody has used MP2-EFP combination. So, please tell me which energy is correct and should be compared with the energy in vacuum. The three options which I see in the log file are :

Energy = Solute potential energy + Solute kinetic energy      or
Energy = Total Energy   or
Energy = Total Energy - Effective Fragment Energy

This is how the energy values look like in an MP2-EFP calculation

               ONE ELECTRON ENERGY =   -5521.7840543068
               TWO ELECTRON ENERGY =    2405.7150238918
          NUCLEAR REPULSION ENERGY =    2049.8047313555
         EFFECTIVE FRAGMENT ENERGY =      -7.6260095839
                                     ------------------
                      TOTAL ENERGY =   -1073.8903086434

ELECTRON-ELECTRON POTENTIAL ENERGY =    2405.7150238918
 NUCLEUS-ELECTRON POTENTIAL ENERGY =   -6587.0748922130
  NUCLEUS-NUCLEUS POTENTIAL ENERGY =    2049.8047313555
ELECTRON-FRAGMENT MULTIPOLE ENERGY =       0.4295428235
ELECTRON-FRAGMENT REMAINDER ENERGY =      -0.0600891940
       STATIC INTERFRAGMENT ENERGY =      -5.1078075649
           FRAGMENT-NUCLEAR ENERGY =      -0.4524465268
   TOTAL FRAGMENT INDUCTION ENERGY =      -2.0717456091
                                     ------------------
            TOTAL POTENTIAL ENERGY =   -2138.8176830370
                                     ------------------
           SOLUTE POTENTIAL ENERGY =   -2131.5551369657
             SOLUTE KINETIC ENERGY =    1064.9273743936
                VIRIAL RATIO (V/T) =       2.0015967175