On Thursday 05 May 2005 17:43, Eyvaz Isaev wrote: > Actually, the error means that the Ewald sum (ion-ion > energy contribution) could not converge for some > reason. I have to remind that the Ewald sum consists > of two parts: erf(\alpha R)/R and erfc(\alpha R)/R. > The first term has a fast convergence in G-space, > while the second term converges in R-space. > There are also 2 \alpha-dependent contributions, > excluded from sums. > Optimum \alpha has to be chosen so that it gives good > convergence for both G-, and R- sums.
the exact meaning of the error is that the code (PW/ewald.f90) could not determine a value for alpha giving a converged G-space sum for the available set of G-vectors. "Optimal" is somewhat misleading in this respect. The only reasons for such error I can think of, iare either a very weird structure, or an exceedingly low cutoff Paolo -- Paolo Giannozzi e-mail: giannozz at nest.sns.it Scuola Normale Superiore Phone: +39/050-509876, Fax:-563513 Piazza dei Cavalieri 7 I-56126 Pisa, Italy
