# [molpro-user] Gradients with lattice charges

Aaron Virshup aaron at spawn.scs.uiuc.edu
Tue Sep 20 17:35:21 BST 2005

```Hello molpro users,

I have been using a system with lattice charges, and the gradients on my
molecules don't seem to include the force from the lattice charges.

In the example below, a lattice charge near a hydrogen atom has a
violating Newton's 3rd law.

Here is the relevant part of the input deck:
---------------
geometry={
nosymm,noorient
H,, 0.0, 0.0, 0.0
}
basis=6-31g**

int
lat,10.0, 0.0, 0.0, 10.0
hf
forces,lattice=2
----------------

Here are the forces from the output:
---------------
1PROGRAM * Lattice forces     Author: F R Manby (2002)

Number of lattice points:            1

0.000000000000000       0.000000000000000

1PROGRAM * FORCE (Gradient of the energy)

Orbitals from record         2100.2

Number of active orbitals:        1 (  1 )
Number of occupied orbitals:      1 (  1 )

Number of electrons= 1     Doublet     Space symmetry=1
Wavefunction type: OSCF

End of calculation of the energy gradient  ,IREST=   0

Atom          dE/dx               dE/dy               dE/dz

1         0.000000000         0.000000000         0.000000000
-----------------
As you can see, the hydrogen exerts a force on the lattice charge, but
the lattice charge does not exert an equal and opposite force on the
hydrogen.

Does anyone know of a way to get around this, aside from numerical

Thanks,
Aaron

--
============================================================
Aaron Virshup                                 Martinez Group
Department of Physics                    Phone: 217-244-7383
University of Illinois at Urbana-Champaign
1110 W. Green St.
Urbana, IL 61801                    aaron at spawn.scs.uiuc.edu
============================================================

```