How can I estimate the uncertainty on a calculated energy value?

[Vladimir Rybkin]

Dear Cristiana,

the question has no correct answer. To give a few points:
1) the energy here is in Hartree (that's the only thing for sure here)
2) the energy itself is meaningless, what is reported is the energy 
difference. In kJ/mol people report them with one digit, which, however 
does not mean that the uncertainty is 0.05. It's just a convention.
3) try to find benchmarks on your systems and use the recommended methods 
with estimated accuracy.

Yours,

Vladimir

понедельник, 24 апреля 2017 г., 10:55:29 UTC+2 пользователь Cristiana 
Passiu написал:
>
> Dear all,
> assuming that a model is correct and that the functional chosen is 
> suitable for the system, is there a standard uncertainty that can be 
> attributed to the final energy values? In other words, how many 
> significative digits can I report in the results?
>
> What is the default unit of measurement for the energy in the output? For 
> example, if I have this in the output:
>
>   Total energy:                                             
>  -158.42425955059213
>  ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):             
> -158.424259550592126
>
> are the values in Rydberg or in Hartree? In order to convert them to eV, 
> do I have to multiply them by 27.2113838668?
>
> Many thanks,
> Cristiana
>
>
>
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