The functional is the same but the approach used to reach the solution is different. PWscf uses a self-consistent cycle technique while ensemble DFT recast it in a global-minimization problem.
Ensemble DFT is guaranteed (if I remember correctly) to be a scheme where the total energy decreases at each iteration while for the self-consistent solution sometime the energy does not monotonically decrease with the number of iteration before converging. I think that the relative efficiency of the two methods may be different for different systems and only experience can tell you wich one is more efficient for your system. Tricky systems are typically very anisotropic metallic slabs subjects to charge sloshing (dealt with mixing_mode='local-TF' in PWscf) and/or magnetic systems where many alternative solutions are close in energy (larger smearing usually helps in stabilizing the system but may wash out the physical effect... very many kpoints and a small smearing may be needed) . In these cases the always decreasing nature of ensembe-DFT may be useful. At variance with CP, PWscf exploits symmetry so for "crystals" PWscf may be preferable. I don't know how the many-k-points case, often needed for metals, is dealt with in the ensemble DFT method... in principle all partially occupied electronic states (nbnd*nks) should be treated together. But I don't know how this is done in CP. Methfessel and Paxton broadening may leads to non positive-definite occupation numbers. This is usually not a big problem for PWscf , when decent k-point sampling is used, but I think it is incompatible with the ensemble DFT scheme. Luckily other efficient smearing techniques such as the Marzari-Vanderbilt scheme are available that are positive-definite. Stefano de Gironcoli - SISSA and DEMOCRITOS Eduardo Ariel Menendez Proupin wrote: > Hi, > I am curious about the difference between the ensemble DFT method > implemented in CP and the smeared DFT used in PWSCF with > Methfessel-Paxton smearing. ?What is better for what system? > > -- > Eduardo Menendez > Departamento de Fisica > Facultad de Ciencias > Universidad de Chile > Phone: (56)(2)9787439 > URL: http://fisica.ciencias.uchile.cl/~emenendez > <http://fisica.ciencias.uchile.cl/%7Eemenendez> > ------------------------------------------------------------------------ > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >
