# Help,how can I get the potential energy of each atom in a structure using DFT package

1. Mar 14, 2012

### wkxez

I am a freshman in DFT calculation. I don't understand the DFT method clearly,but I want to use DFT to do some calculations.
My question is that how how can I get the potential energy of each atom in a structure using DFT package ,which I have done by using classical MD method in Lammps(the command: compute 1 all pe/atom ,Lammps manual :The per-atom energy is calculated by the various pair, bond, etc potentials defined for the simulation. If no extra keywords are listed, then the potential energy is the sum of pair, bond, angle, dihedral,improper, and kspace energy.).
I want to know how can I do such a calculation.Please give some suggestions.

2. Mar 15, 2012

### wkxez

Re: help,how can I get the potential energy of each atom in a structure using DFT pac

I now know that i can get the force F of each atom from the results of vasp relaxation calculation .In the classical theory,F= dU/dr(U is the potential energy),,so if it's possible to get the potential energy from the VAsp or other package calculation?

3. Mar 15, 2012

### Useful nucleus

Re: help,how can I get the potential energy of each atom in a structure using DFT pac

The notion of energy per atom is ill defined for a non-crystalline material. IF you are modelling a crystal , you simply divide the total energy by the number of unit formulas of the crysta.

4. Mar 18, 2012

### wkxez

Re: help,how can I get the potential energy of each atom in a structure using DFT pac

Thank you for your reply,Why is it ill defined for non-crystalline material? And you may misunderstand my question. I want to get the relative potential energy of each atom in a structure,not energy per atom.

5. Mar 19, 2012

### DrDu

Re: help,how can I get the potential energy of each atom in a structure using DFT pac

In an infinite solid this is difficult, in a molecule you can in principle remove that atom from the calculation and compare the energy of the molecule with and without the atom. In practice there is a problem called basis set superposition error, and you may have to replace the atom by a ghost atom with the same basis set but zero nuclear charge.
For a solid you would have to consider probably some large super cell.