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

Benjamin Hourahine benjamin.hourahine at strath.ac.uk
Wed Aug 28 18:24:52 CEST 2019

Hello Vladimir,

What I think you might need is Ehrenfest dynamics.

There is a pull request ( https://github.com/dftbplus/dftbplus/pull/146
) for the fixed nuclei electron dynamics, as developed by the Sánchez
group. This should be incorporated for the next release later this year.
The full nuclear and electron dynamics are currently under development,
and will include transfer of energy from laser or other fields into the
electronic degrees of freedom.



On 28/08/2019 15:52, Lipp, Vladimir wrote:
> Dear Ben,
> Thank you for your reply!
> Yes, I need to specify the kinetic energy of the electrons. My simulation starts with Te=300 K and I am slowly adding energy to the electrons. I know how much energy I will add, but I don't know which temperature will be reached. The corresponding temperature will of course oscillate with the atomic motion; this is expected for the NVE ensemble. But the energy should not oscillate as there is no thermostat or exchange of the energy with anything.
> Currently, the electron energy is oscillating instead, which prevents me from achieving the energy conservation. The electron temperature may reach a very high value in my case (let's say 1.5 eV in diamond or more), I clearly see the problem coming from the TS term. Is this possible to calculate the forces from U, not U-TS?
> Vladimir
> ----- Original Message -----
> From: "Benjamin Hourahine" <benjamin.hourahine at strath.ac.uk>
> To: "dftb-plus-user" <dftb-plus-user at mailman.zfn.uni-bremen.de>
> Sent: Wednesday, 28 August, 2019 15:59:46
> Subject: Re: [DFTB-Plus-User] How to specify electronic energy in the input?
> 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.
> Regards
> Ben
> without the electron entropy correction
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       Dr. B. Hourahine, SUPA, Department of Physics,
     University of Strathclyde, John Anderson Building,
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