# QuantumATK Forum

## QuantumATK => General Questions and Answers => Topic started by: narin on August 15, 2022, 19:36

Title: How does QuantumATK calculate the kinetic energy?
Post by: narin on August 15, 2022, 19:36
Dear Sirs,

How does QuantumATK calculate the kinetic energy? I looked the help page and the manual but couldn't find any formula.

Thanks.
Title: Re: How does QuantumATK calculate the kinetic energy?
Post by: AsifShah on August 16, 2022, 07:01
Calculate total energy & look for log file. There will be all energy contributions.
Title: Re: How does QuantumATK calculate the kinetic energy?
Post by: Umberto Martinez on August 16, 2022, 09:03
and to extract from an MD, you can use the Kinetic Energy Distribution from the MD analyzer:
https://docs.quantumatk.com/manual/Types/KineticEnergyDistribution/KineticEnergyDistribution.html
Title: Re: How does QuantumATK calculate the kinetic energy?
Post by: filipr on August 16, 2022, 12:11
For DFT the kinetic energy is calculated as in any other DFT code (see e.g. https://en.wikipedia.org/wiki/Density_functional_theory and https://en.wikipedia.org/wiki/Kohn%E2%80%93Sham_equations):

T = ⟨T⟩ = ∑n fn ⟨ψn| -ħ2/(2m)∇2n

where fn is the occupation number of the n'th state and |ψn⟩ are the Kohn-Sham states.
Title: Re: How does QuantumATK calculate the kinetic energy?
Post by: narin on August 16, 2022, 18:27
Thanks a lot for your replies.