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

Quan Phung manhquank9 at gmail.com
Tue Apr 8 19:53:28 BST 2014

```Hello,

As I mentioned above, Molpro does not include the interaction between the
point charges, which is 1.0145591 Ha.
The interaction between Fe (nucleus charge +26) and the point charge (-1)
is -27.56070553 Ha, which is computed correctly by Molpro.
So total = -26.54614640 Ha.

Best regards,
Quan

On Tue, Apr 8, 2014 at 10:16 AM, Susi Lehtola <
susi.lehtola at alumni.helsinki.fi> wrote:

> On Tue, 8 Apr 2014 09:36:09 +0300
> 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...
>
> The numbers do seem really weird. First, the nuclear repulsion energy
> doesn't depend on the electronic structure. Second, electronic
> contributions for iron would be much larger than a few dozen Hartree.
> But the number is really big to be purely Coulombic.
>
> Computing the numbers by hand I get
>
> - repulsion of the point charges: 1.0145 Ha
> - attraction of point charges and nucleus: -1.060 Ha
> total: -0.0455 Ha
>
> If you compute the difference between the Molpro and Orca numbers, you
> get the difference of 1.0145591 Ha, which you see is the repulsion of
> the point charges.
>
> I'm guessing Molpro doesn't include the static repulsion of the point
> charges in the energy it computes.
> --
> ---------------------------------------------------------------
> 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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>
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