# Re: [SIESTA-L] Total energy

```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,

Â  Â Kresse & FurthmÃ¼ller, 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:
> ThanksÃ‚Â  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
>
> siesta: Program's energy decomposition (eV):
> siesta: Ebs Ã‚Â  Ã‚Â  = Ã‚Â  Ã‚Â  Ã‚Â -859.157108
> siesta: Eions Ã‚Â  = Ã‚Â  Ã‚Â  Ã‚Â 9568.777238
> siesta: Ena Ã‚Â  Ã‚Â  = Ã‚Â  Ã‚Â  Ã‚Â  277.651800
> siesta: Ekin Ã‚Â  Ã‚Â = Ã‚Â  Ã‚Â  Ã‚Â 4247.415878
> siesta: Enl Ã‚Â  Ã‚Â  = Ã‚Â  Ã‚Â  -1698.956164
> siesta: Eso Ã‚Â  Ã‚Â  = Ã‚Â  Ã‚Â  Ã‚Â  Ã‚Â  0.000000
> siesta: Edftu Ã‚Â  = Ã‚Â  Ã‚Â  Ã‚Â  Ã‚Â  0.000000
> siesta: DEna Ã‚Â  Ã‚Â = Ã‚Â  Ã‚Â  Ã‚Â  162.636813
> siesta: DUscf Ã‚Â  = Ã‚Â  Ã‚Â  Ã‚Â  Ã‚Â 26.981770
> siesta: DUext Ã‚Â  = Ã‚Â  Ã‚Â  Ã‚Â  Ã‚Â  0.000000
> siesta: Exc Ã‚Â  Ã‚Â  = Ã‚Â  Ã‚Â  -6715.533109
> siesta: eta*DQ Ã‚Â = Ã‚Â  Ã‚Â  Ã‚Â  Ã‚Â  0.000000
> siesta: Emadel Ã‚Â = Ã‚Â  Ã‚Â  Ã‚Â  Ã‚Â  0.000000
> siesta: Emeta Ã‚Â  = Ã‚Â  Ã‚Â  Ã‚Â  Ã‚Â  0.000000
> siesta: Emolmec = Ã‚Â  Ã‚Â  Ã‚Â  Ã‚Â  0.000000
> siesta: Ekinion = Ã‚Â  Ã‚Â  Ã‚Â  Ã‚Â  0.000000
> siesta: Eharris = Ã‚Â  Ã‚Â Ã‚Â  -13268.580292
> siesta: Etot Ã‚Â  Ã‚Â = Ã‚Â  Ã‚Â  Ã‚Â Ã‚Â  -13268.580250
> siesta: FreeEng = Ã‚Â  Ã‚Â -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:
>
>
>>Â  Â  Â On 20 Jun 2022, at 17:16, Francisco Garcia
<garcia.ff....@gmail.com <mailto:garcia.ff....@gmail.com>
>>Â  Â  Â <mailto:garcia.ff....@gmail.com
<mailto:garcia.ff....@gmail.com>>> wrote:
>>
>>Â  Â  Â Dear users,
>>
>>Â  Â  Â In metallic systems with a fairly sizable electronic smearing
temperature
>>Â  Â  Â T, is it accurate to claim that
>>
>>Â  Â  Â (i) in a single point calculation, the free energy is the
representative
>>Â  Â  Â energy of the system (due to the addition of -TS to the total
energy U)
>
>Â  Â  Â No, the -TS term for the phononic entropy is missing.Ã‚
>
>Â  Â  Â It is the free energy defining the finite temperature equilibrium
for the
>Â  Â  Â purely electronic
>Â  Â  Â problem for fixed external potential (fixed nuclei), as in
MerminÃ¢â‚¬â„¢s finite
>Â  Â  Â -T DFT.
>
>
>>Â  Â  Â (ii) in a variable cell optimization, the enthalpy is the
representative
>>Â  Â  Â energy of the system (due to the addition of the PV term to the
energy).
>
>Â  Â  Â Yes, it is the free energy of the system (minimum defines
equilibrium) for T=0.
>
>Â  Â  Â Emilio
>
>>
>>Â  Â  Â Thanks!
>>Â  Â  Â Ã‚
>>
>>Â  Â  Â --
>>Â  Â  Â SIESTA is supported by the Spanish Research Agency (AEI) and by
the
>>Â  Â  Â European H2020 MaX Centre of Excellence
(http://www.max-centre.eu/)
>
>Â  Â  Â --
>Â  Â  Â Emilio Artacho
>
>Â  Â  Â Theory Group, Nanogune, 20018 SanÃ‚Â Sebastian, Spain, and
>Â  Â  Â Theory of Condensed Matter,Ã‚Â Department of Physics,
>Â  Â  Â Cavendish Laboratory, University ofÃ‚Â Cambridge, Cambridge CB3
0HE, UK
>
>
>
>
>
>Â  Â  Â --
>Â  Â  Â SIESTA is supported by the Spanish Research Agency (AEI) and by
the European
>Â  Â  Â H2020 MaX Centre of Excellence (http://www.max-centre.eu/)
>
>
>

```
-- Dr. Roberto C. PasianotÂ  Â  Â  Â  Â Phone: 54 11 4839 6709
```    Gcia. Materiales, CAC-CNEAÂ  Â  Â  FAXÂ  : 54 11 6772 7362
Avda. Gral. Paz 1499Â  Â  Â  Â  Â  Â 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/)
```