[molpro-user] question about energy scale

[Andreas Hesselmann]

Dear Yusuke,

probably you could use the DFT-SAPT program
implemented in Molpro for what you intend to do
(it will not work if one of the two monomers
is an open-shell system, however).
In DFT-SAPT the total interaction energy is
a sum of electrostatic, induction, dispersion
and corresponding exchange interaction contributions.
The exchange interactions are those terms that 
would be nearly zero in your case if you
increase the distance of the two atoms.
Dipole-dipole interactions would be a part
of the electrostatic interaction energy due
to charge penetration effects.

It is hard to tell if it would be possible
to achieve accuracies of 10^(-10) Hartrees
in such a calculation because it depends on
some convergence thresholds (for energy, 
density matrix, quadrature,...). I remember
that we were able to very accurately reproduce
the Helium dimer electrostatic interaction energy
with up to 10^(-3) microHartree accuracy
using DFT-SAPT and an exact xc potential
(see Phys. Chem. Chem. Phys. 5 (2003) 5010 - 5014).

Best wishes,
Andreas