[Pw_forum] a question about calculating free energy

[Eyvaz Isaev]

Hi,

> the error information:
> "run-time error M6202: MATH
> - log: SING error"
> 
> I also know the negative value appears in log
> function described as the following line,
> "    if (T.gt.0.d0)
> Ftot=Ftot+dos(i)*a2*T*log(1.0d0-exp(-a3*nu(i)/T))
> "
> but I do not know how to resolve this problem.
  
If you have imaginary (negative in your files)
frequences, your system is dynamically unstable, so, 
it is meaningless to calculate the free energy for
such a kind unstable system. 

Bests,
Eyvaz.


		
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