[Thermo_pw-forum] Thermo_pw-forum Digest, Vol 11, Issue 3

[agbaoye at physics.unaab.edu.ng]

Thank you very much i appreciate your kind and quick response, i will try
a better optimized system

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> Today's Topics:
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>    1. Re: result of debye temperature, entropy, free energy and
>       heat capacity returned NaN (Andrea Dal Corso)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 11 Aug 2016 11:37:40 +0200
> From: Andrea Dal Corso <dalcorso at sissa.it>
> Subject: Re: [Thermo_pw-forum] result of debye temperature, entropy,
> 	free energy and heat capacity returned NaN
> To: thermo_pw-forum at qeforge.qe-forge.org
> Message-ID: <1470908260.1808.18.camel at ulisse.cm.sissa.it>
> Content-Type: text/plain; charset="UTF-8"
>
> It seems that your system is unstable. One of the elastic constants C_44
> turns out to be negative. In this case the speed of sound gives NaN
> because the code takes the square root of a negative number.
>
> There are three possibilities:
> 1) your system is actually stable but you are simulating it with too few
> k points, too low cut-off etc. So increasing the computational accuracy
> may transform it into a stable system.
>
> 2) your system is really unstable and the code cannot solve this
> situation.
>
> 3) there is still a problem in the calculation of elastic constants and
> some error occurs in the calculation of C_44. I will investigate this
> possibility.
>
> In any case, thank you for reporting this. I will remove the printing of
> NaN.
>
> HTH,
>
> Andrea
>
>
>
> On Tue, 2016-08-09 at 08:40 +0200, agbaoye at physics.unaab.edu.ng wrote:
>> Good day to everyone
>>
>> I did some scf_eleastic_constant and mur_lc_elastic_constants
>> calculations
>> on thermo_pw but the result of entropy, free energy heat capacity and
>> energy result data returned NaN also making the debye temperature return
>> a
>> NaN value. I have tried to figure it out but i am not sure of the cause
>> of
>> this anomaly and the possible solutions.
>> I will be glad if this anomaly can be resolved
>>
>> Thank you
>>
>> Agbaoye Ridwan Olamide
>> Federal University of Agriculture, Abeokuta
>>
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> --
> Andrea Dal Corso                    Tel. 0039-040-3787428
> SISSA, Via Bonomea 265              Fax. 0039-040-3787249
> I-34136 Trieste (Italy)             e-mail: dalcorso at sissa.it
>
>
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> End of Thermo_pw-forum Digest, Vol 11, Issue 3
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