[DFTB-Plus-User] about total energy

Ben Hourahine benjamin.hourahine at strath.ac.uk
Mon Aug 1 23:41:43 CEST 2016

Hello Cuihong,

The total energy is the sum of the electronic and repulsive potential
energies (and dispersion if present). The Mermin free energy includes
the electronic entropy, but no other contributions. The Helmholtz energy
(printed out for non-zero pressure) is the Mermin energy plus pV.

To get an estimate of the Gibbs free energy, methods such as umbrella
sampling, thermodynamic integration, harmonic approximations or REMD are
required. These are not currently supported within DFTB+, but can be
accessed via some of the codes that can externally drive DFTB+. These
include i-Pi (an interface will be available in the 1.3 DFTB+ release)
or ASE.



On 30/07/16 05:19, 王翠红 wrote:
> Hello everyone,
>      I have a question about the Total energy, what is the meaning of total energy? Is it the free energy or the potential energy? If it is the free energy, assuming no change in temperature (T) and volume, the change in free energy is given by delG = delH - T.delS, where delH is equivalent to the change in internal energy, and delS represents the entropic change in the system. Is it only considered the delH?
> Thank you very much.
> Best,
> Cuihong
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