[molpro-user] Lattice point of charges in Molpro vs Orca

[Quan Phung]

Dear Susi,

Thank you.
Yes, it is Fe2+, not Fe. However, since I put 4 negative point charges, the
nuclear repulsive energy should be negative.
Prof. Fred Manby has answered my question. In Molpro, the interaction
between point charges are ignored, as it is normally handled in an MM code,
while other QM codes include this interaction.

The input I gave is just a toy model, as CASSCF will be done to check the
wavefunction.

Best regards,
Quan



On Tue, Apr 8, 2014 at 8:36 AM, Susi Lehtola <
susi.lehtola at alumni.helsinki.fi> wrote:

> On Mon, 7 Apr 2014 21:20:22 +0200
> Quan Phung <manhquank9 at gmail.com> wrote:
> > Dear Molpro users,
> >
> > I'm trying to calculate Fe atom with 4 surrounding point charges.
> > The nuclear repulsion energy by Molpro is  -27.56070553 Ha.
> > However, both Orca and Molcas give -26.54614640 Ha.
> > Did I do something wrong?
>
> First, you seem to be calculating Fe^{2+}, not Fe. Second, the nuclear
> repulsion energy should be positive. Anyway...
>
> Transition metals are notoriously difficult for single-determinant
> calculations. The wave function space is laden with saddle point
> solutions, and it is extremely difficult to converge even to a local
> minimum. I remember trying to toy around with point charges to lift
> this degeneracy, but didn't get anywhere.
>
> You really need to run a stability analysis before you can trust the
> numbers you are getting.
> --
> ---------------------------------------------------------------
> Mr. Susi Lehtola, PhD             Research Associate
> susi.lehtola at alumni.helsinki.fi   Department of Applied Physics
> http://www.helsinki.fi/~jzlehtol  Aalto University
>                                   Finland
> ---------------------------------------------------------------
> Susi Lehtola, FT                  Tutkijatohtori
> susi.lehtola at alumni.helsinki.fi   Fysiikan laitos
> http://www.helsinki.fi/~jzlehtol  Aalto-yliopisto
> ---------------------------------------------------------------
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