On Saturday, October 15, 2016 12:02:51 PM CEST Zara Nosh wrote: > Using vdw-df we should use rev-pbe pseudopotential but > it seems that my results from blyp+vdw-df is better that revpbe+vdw-df. > > Can we use blyp pseudopotentials with vdw-df?
Dear Zara, Technically you can, but then you'll have to justify it to the referee of your paper who may not be too keen to accept it. Vdw-df uses the revPBE formulation for the XC functionals, if you use anything else just because it fits better with what you wish to obtain, it is just because of a fortunate cancellation of errors: you're not doing an ab-initio calculation anymore. Some amount of arbitrariness, or non-ab-initio fitting, may be inevitable even in a DFT calculation, some examples: 1. choosing the experimental lattice parameter instead of the optimized one; 2. fitting the value of U in LDA+U, instead of computing it abinitio 3. fitting the fraction of the Fock exchange in a Hybrid functional calculation 4. using a pseudopotential for a different flavour of the XC functional than the one used in you calculation My personal opinion is: 1. acceptable if the optimized value gives completely off results, and using a more advanced method is not feasible 2. acceptable if computing the value of U abinitio is impossible (e.g. too expensive) 3. not acceptable, unless you're using HSE, in which case I have no idea 4. not acceptable, because as doing thigs properly is no more expensive and because I cannot find any plausible justification for it HTH -- Dr. Lorenzo Paulatto IdR @ IMPMC -- CNRS & Université Paris 6 phone: +33 (0)1 44275 084 / skype: paulatz www: http://www-int.impmc.upmc.fr/~paulatto/ mail: 23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05 _______________________________________________ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum