Re: [SIESTA-L] Total energy

[RCP]

Hi again,

On 22/06/2022 19:27, Francisco Garcia wrote:

Thank you very much for the reference!Â

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

Sure, because semiconductors do have an energy gap. Smearing (i.e. electronic
temperature) is just a trick used for metals in order to smooth their Fermi
surface so that some BZ integrals become easier to perform.
Take care,
Roberto

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 <mailto: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>
     > <mailto: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>
     >>     <mailto: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.Â
     >
     >     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!
     >>     Â
     >>
     >>     --
     >>     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
    <mailto: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/)