[Pw_forum] a question about calculating free energy

Eyvaz Isaev eyvaz_isaev at yahoo.com
Wed Jul 27 07:37:36 CEST 2005


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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