How can I estimate the uncertainty on a calculated energy value?
uido... at libero.it
Thu May 11 16:41:26 CEST 2017
thank you for your reply and for the interesting paper suggested.
Il giorno giovedì 11 maggio 2017 11:59:30 UTC+2, Filipe Teixeira ha scritto:
> In the early 2000's Irikura introduced the concept of "virtual
> meassurement" (J. Phys. Chem. A, 2005, 109, 8430). In this article one of
> the sources of error he explored is the error associated with the SCF of
> optimied geometries (which may depend, for example on the initial geometry
> being optimized and the propagation of numerical errors in the SCF
> procedures). It is an interesting reading if you are interested on that
> matter, but (spoiller allert) those errors (even in 2005 when 32-bit
> machines were common) are minor compared to the errors of the methodologies
> themselves. Nowadays, with 64-bit machines being the norm, I doubt machine
> round-up will be a big source of error for most applications...
> I hope this helps.
> Best regards,
> Filipe Teixeira
> On Wednesday, May 10, 2017 at 12:42:45 PM UTC+1, Cristiana Passiu wrote:
>> Dear Vladimir,
>> thank you for your answer. It will be helpful for knowing how to express
>> the results of the calculations.
>> Best regards,
>> Il giorno mercoledì 10 maggio 2017 10:07:57 UTC+2, Vladimir Rybkin ha
>>> 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.
>>> 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:
>>>> ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):
>>>> 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,
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