[QE-users] (no subject)

[Giovanni Cantele]

Dear Nirmal,

there can be several reasons why you find such a (possibly strange) behaviour. 
I give you two possible reasons, that I can easily explain.
One is that one of the two calculations (or both) is (are) wrong, but this point might be better assessed if you provide the inputs of both calculation. 
The second is that the two calculations are NOT carried out within the same framework. The point is that in plane-waves calculations the total energy is meaningless. It is enough that you change pseudopotentials, and the total energy might change by many Ry! Again, the inputs could be helpful in understanding if this is the case.
Much better, to compare two different calculations, are the energy differences. For example, in you MD simulation, you could have an initial and a final geometry, and you can compute the energy difference between the two.
You could then input both geometries in a scf calculation, and compute again their energy difference.
The two differences, should at least look similar, otherwise you can conclude that something wrong is affecting your results.

Giovanni

> On 23 Feb 2022, at 15:55, Nirmal Barman <nirmalbarmanphysics at gmail.com> wrote:
> 
> Dear Quantum Espresso Users and Developers,
> I have calculated scf energy for a graphene sheet and obtained the value -205.39676576 Ry. But this scf energy is not matching or close to the energy obtained at different steps of MD simulation. There is a significant deviation in magnitude as well as energy is positive in case of MD simulation. Could you please tell me the reason? Ideally this scf energy should mimic the MD simulated result.
> 
> Thanking you
> Best regards 
> Nirmal
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