Thank you very much for the reference! I'll use E=1/2(Etot +FreeEng) for my E-V equation of state fit.
I noticed that for semiconductors, Etot = FreeEng; it is in metallic systems that I see differences between Etot and FreeEng (with FreeEng being lower). In this regard, using the average of the two energies for T=0 makes sense. Thanks again! On Wed, Jun 22, 2022 at 3:01 PM RCP <pasia...@cnea.gov.ar> wrote: > Hello, > May I contribute my 0.01 ?. According to Eq.(21) in, > > Kresse & Furthmüller, Comp. Mat. Sci. 6 (1996) 15-50 > > a good estimate for the (T=0K) DFT energy is 1/2(Etot +FreeEng), and > this is the recipe I've always used. > > Regards, > Roberto > > On 22/06/2022 13:11, Francisco Garcia wrote: > > Thanks for your response Prof. Artacho! > > > > So if I have a situation like below for a large metallic system in which > FreeEng > > is lower than Etot, should I use Etot? Specifically, if I want to plot > the E-V > > curve from single point runs to obtain the equation of state I should > use Etot > > instead of FreeEng? Or if I want to compute the cohesive energy, Etot > should be > > used instead of FreeEng? > > > > siesta: Program's energy decomposition (eV): > > siesta: Ebs   =    -859.157108 > > siesta: Eions  =    9568.777238 > > siesta: Ena   =    277.651800 > > siesta: Ekin   =    4247.415878 > > siesta: Enl   =   -1698.956164 > > siesta: Eso   =     0.000000 > > siesta: Edftu  =     0.000000 > > siesta: DEna   =    162.636813 > > siesta: DUscf  =     26.981770 > > siesta: DUext  =     0.000000 > > siesta: Exc   =   -6715.533109 > > siesta: eta*DQ  =     0.000000 > > siesta: Emadel  =     0.000000 > > siesta: Emeta  =     0.000000 > > siesta: Emolmec =     0.000000 > > siesta: Ekinion =     0.000000 > > siesta: Eharris =    -13268.580292 > > siesta: Etot   =     -13268.580250 > > siesta: FreeEng =   -13269.911499 > > > > On Tue, Jun 21, 2022 at 2:07 PM Emilio Artacho <e.arta...@nanogune.eu > > <mailto:e.arta...@nanogune.eu>> wrote: > > > > > >> On 20 Jun 2022, at 17:16, Francisco Garcia <garcia.ff....@gmail.com > >> <mailto:garcia.ff....@gmail.com>> wrote: > >> > >> Dear users, > >> > >> In metallic systems with a fairly sizable electronic smearing > temperature > >> T, is it accurate to claim that > >> > >> (i) in a single point calculation, the free energy is the > representative > >> energy of the system (due to the addition of -TS to the total > energy U) > > > > No, the -TS term for the phononic entropy is missing. > > > > It is the free energy defining the finite temperature equilibrium > for the > > purely electronic > > problem for fixed external potential (fixed nuclei), as in > Mermin’s finite > > -T DFT. > > > > > >> (ii) in a variable cell optimization, the enthalpy is the > representative > >> energy of the system (due to the addition of the PV term to the > energy). > > > > Yes, it is the free energy of the system (minimum defines > equilibrium) for T=0. > > > > Emilio > > > >> > >> Thanks! > >>  > >> > >> -- > >> SIESTA is supported by the Spanish Research Agency (AEI) and by the > >> European H2020 MaX Centre of Excellence (http://www.max-centre.eu/) > > > > -- > > Emilio Artacho > > > > Theory Group, Nanogune, 20018 San Sebastian, Spain, and > > Theory of Condensed Matter, Department of Physics, > > Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK > > > > > > > > > > > > -- > > SIESTA is supported by the Spanish Research Agency (AEI) and by the > European > > H2020 MaX Centre of Excellence (http://www.max-centre.eu/) > > > > > > > > -- > Dr. Roberto C. Pasianot Phone: 54 11 4839 6709 > Gcia. Materiales, CAC-CNEA FAX : 54 11 6772 7362 > Avda. Gral. Paz 1499 pasia...@cnea.gov.ar > 1650 San Martin, Buenos Aires > ARGENTINA >
-- SIESTA is supported by the Spanish Research Agency (AEI) and by the European H2020 MaX Centre of Excellence (http://www.max-centre.eu/)
