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dear all

I am so confused by the three type of energy.
The physics meaning of them is clear, but i just don't know how to chose the suitable one .

is there any correlation between the suitable choice and the parameters in the INCAR , such as ISMERA and IBRION?

furthermore, is there any difference between energy without entropy and energy(sigma->0)? in my opinion, when sigma->0 ,the entropy is zero.
however, in many calculations , energy without entropy and energy(sigma->0) are not equal

Thanks
<span class='smallblacktext'>[ Edited ]</span>

[quote="dyc_2008"]
furthermore, is there any difference between energy without entropy and energy(sigma->0)? in my opinion, when sigma->0 ,the entropy is zero. however, in many calculations , energy without entropy and energy(sigma->0) are not equal
[/quote]
For energy (sigma->0), I think there is an extrapolation formula to estimate the value of the total energy corresponding to sigma=0 by using a sigma>0 result. The total energy without entropy simply subtracts the electronic thermal energy away from the calculated total energy.

that is a very brilliant interpretation
thank you so much

I could use some help with this. In the O atom example on the Wiki, it says to use the "energy without entropy" for atoms and molecules. Other sources say use the sigma>0 approx always. This becomes especially important in desorption calculations where we are taking differences between systems using fermi smearing and gaussian smearing.

Can someone enlighten me on this issue?

SIGMA should be primarily considered as a "technical" parameter for the integration into the Brillouin zone. In some cases, like the O atom, the entropy term can be much larger (than in bulk metals) and become unphysical (see wiki/index.php/O_atom). Note also that the default value of SIGMA is 0.2 eV, which corresponds to a temperature of about 2000 K.

You can also have a look at ISMEAR.