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

[Susi Lehtola]

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
---------------------------------------------------------------