[DFTB-Plus-User] How to specify electronic energy in the input?

Benjamin Hourahine benjamin.hourahine at strath.ac.uk
Wed Aug 28 15:59:46 CEST 2019

Hello Vladimir,

What do you mean by specifying the energy of the electrons? The internal
electronic energy (and hence the Mermin free energy) is a functional of
the coordinates of the atoms, so will change on moving atoms about. Or
are you asking if there is a way to set the kinetic energy of the
electrons above the zero temperature ground state?

The internal energy and also the extrapolated zero temperature energy is
available in the output (depending on how you are calling DFTB+, this
might already be directly available to you now).  The reason for
returning the Mermin energy (at the specified temperature) is that the
Helman-Feynmann forces are the derivative of this energy and not the
other cases.

Unless your system is either at very high temperature or has a very
unusual electronic structure, the Mermin TS term is very small.



without the electron entropy correction

On 28/08/2019 14:44, Lipp, Vladimir wrote:

> Hello everyone,
> I have my own molecular dynamics code and I am calling DFTB+ "static calculation" every time step to provide me the forces. 
> When calling DFTB+, one can specify the electron temperature in the Fermi distribution; however, in this case, DFTB+ assumes that the electronic temperature is constant and uses Mermin Free energy to calculate the forces. I do not want to have constant-temperature electrons, I rather need to specify their energy and get electron-energy-related forces. In other words, I need NVE ensemble for the electrons. Is this possible?
> Thank you in advance for any response.
> Vladimir Lipp
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     University of Strathclyde, John Anderson Building,
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