[Wien] temperature dependent DFT (band, ...) calculations

Sun Apr 19 18:37:10 CEST 2020

great reply, thanks a lot, lot of things found from your data dear Samuel
B. Trickey.
Stay blessed.

On Sun, Apr 19, 2020 at 12:08 AM Sam Trickey <trickey at qtp.ufl.edu> wrote:

> Regarding the question of temperature effects, let me add some
> remarks about electronic temperature.
>
> Under diverse circumstances (e.g. laser heating) it is possible
> for the electrons and phonons to have very different temperatures
> for experimentally meaningfully long times.   Of course it also is
> possible for the two populations to be at equilibrium at a temperature
> that is high with respect to some important criterion.
>
> In either case, finite-temperature or free-energy DFT can
> be important for calculation.  Free energy DFT has been known since
> Mermin's paper in 1965. Superficially, the computation looks like a
> ground-state Kohn-Sham equation with non-integer Fermi-Dirac
> approximations.
> Often that superficial resemblance has led people to implement calculations
> by taking an ordinary ground state XC functional, e.g. PBE, and stuffing in
> a finite-T density.  For comparatively low electronic temperatures, up to
> several thousand Kelvin (i.e. about 0.75 eV) perhaps, that is reasonably
> OK for equations of state, conductivity, etc.  Above that it is
> not OK (despite some expert opinion to the contrary) and one
> should use exchange-correlation free energy density functional
> approximations.
>
> Our group has worked very intensely on this problem. Details are in
>
> "Status of free-energy representations for the homogeneous electron gas"
> V.V. Karasiev, S.B. Trickey, and J.W. Dufty, Phys. Rev. B 99, 195134 (2019)
>
> "Nonempirical Semi-local Free-Energy Density Functional for Matter Under
> Extreme Conditions:
> V.V. Karasiev, J.W. Dufty, and S.B. Trickey, Phys. Rev. Lett. 120,
> 076401 (2018)
>
> "Importance of Finite-temperature Exchange-correlation for Warm Dense
> Matter Calculations"
> V.V. Karasiev, L. Calder\'in, and S.B. Trickey, Phys. Rev. E 93, 063207
> (2016)
>
> "Accurate Homogeneous Electron Gas Exchange-correlation Free Energy for
> Local Spin-density Calculations"
> V.V. Karasiev, T. Sjostrom, J. Dufty, and S.B. Trickey, Phys. Rev. Lett.
> 112, 076403 (2014)
>
> "Innovations in Finite-Temperature Density Functionals"
> V.V. Karasiev, T. Sjostrom, D.Chakraborty, J.W. Dufty, F.E. Harris, K.
> Runge, and S.B. Trickey, in "Frontiers and Challenges in Warm Dense
> Matter", F. Graziani et al. eds., (Springer, Heidelberg, 2014) 61-85.
>
> References to the other literature are in our papers. All of them are
> downloadable from  www.qtp.ufl.edu/ofdft
>
> Also, some time ago Andreas G\"orling and colleagues at Erlangen worked
> out finite-T exact exchange and gave examples
>    M. Greiner, P. Carrier, and A. G\"orling
>    Phys. Rev. B 81, 155119 [12 pp] (2010)
> and more recently Andreas and his student Trushin have applied it to
> topological phase transitions
>     Egor Trushin and Andreas G\"orling
>     Phys. Rev. Lett. 120, 146401 [5 pp] (2018)
>
> Perhaps this will be helpful.
>
> Peace, Sam
>
>
> On 4/18/2020 11:42 AM, Peter Blaha wrote:
> > [External Email]
> >
> > If you are lucky, yes, but in general, the answer is NO !!!
> >
> > The lattice parameter is only a "mean value", and is a "prerequisite"
> > for a finit temp calculation.
> >
> > But think about: what means "Termperature"  ?
> >
> > It vibrations, which are excited more or less with T. The atoms move
> > around heavily and this can be even anisotropic.
> > And one measures basically an average of a certain quantity while the
> > atoms are vibrating around.
> >
> > Calculating phonons gives you entropy and free energies;
> > Doing properties with temperature dependent average displacements gives
> > you properties at finite T.
> >
> > One example: Physical Review B, 98 (2018), S. 235205.
> >
> >
> > Am 18.04.2020 um 15:33 schrieb Dr. K. C. Bhamu:
> >> Dear Experts,
> >>
> >> Could you please confirm that if I have temperature dependent lattice
> >> parameters, from DFT calculation, then whatever properties like band,
> >> phonon, elastic, ... , I compute will be considered as temperature
> >> dependent ?
> >> Yes, ionic positions should be relaxed what I know.
> >> My own answer would be yes for this query but I need a confirmation.
> >>
> >> It would be a help from computational resources point of view. I do not
> >> want to test the calculation and see the the difference as system is
> >> more computational time demanding.
> >>
> >> Thank you very much.
> >>
> >> Regards
> >> Bhamu
> >>
> >>
> >>
> >> _______________________________________________
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> >>
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> >
> > --
> >
> --------------------------------------------------------------------------
> >
> > Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> > Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
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> >
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> >
> >
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>
> --
>    Samuel B. Trickey
>    QTP, Depts. of Physics and Chemistry
>    2324 New Physics Building
>    Box 118435
>    Univ. of Florida
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>
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-- 
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Assistant Professor
Centre for Advanced Studies in Physics, 1-Church road
G.C University, Lahore, Pakistan.
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