Understanding DFT to Calculate Potential Energy of Atoms

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SUMMARY

This discussion focuses on using Density Functional Theory (DFT) to calculate the potential energy of atoms within a structure. The user seeks guidance on transitioning from classical Molecular Dynamics (MD) methods in LAMMPS, specifically using the command "compute 1 all pe/atom," to DFT calculations, particularly with VASP. Key points include the challenge of defining energy per atom in non-crystalline materials and the suggestion to utilize supercells for solid-state calculations. The conversation emphasizes the importance of understanding the basis set superposition error when attempting to isolate the energy contributions of individual atoms.

PREREQUISITES
  • Understanding of Density Functional Theory (DFT) principles
  • Familiarity with VASP (Vienna Ab-initio Simulation Package)
  • Knowledge of Molecular Dynamics (MD) simulations using LAMMPS
  • Concept of basis set superposition error in quantum chemistry
NEXT STEPS
  • Learn how to perform DFT calculations using VASP for potential energy analysis
  • Research the concept of supercells in solid-state physics
  • Study the basis set superposition error and its implications in DFT calculations
  • Explore methods for calculating relative potential energy in non-crystalline materials
USEFUL FOR

Researchers and students in computational chemistry, materials science, and solid-state physics, particularly those interested in DFT calculations and potential energy analysis of atomic structures.

wkxez
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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.
 
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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?
 


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.
 


Useful nucleus said:
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.


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.
 


wkxez said:
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.

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.
 

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