Thank Prof. Marzari you for pointing me in the right direction. I also looked up the lectures.
And I'm ansciously waitng for the the https://molmod.ugent.be/deltacodesdftto get back online. On 10/23/2014 11:40 AM, Nicola Marzari wrote: > > Dear Elliot, > > Problem 1------------ > the trend LDA < PBEsol < PBE is typical, so it all looks good. > The two questions are: > > 1) VERIFICATION: is e.g. my PBE result, done with pseudopotentials, > correct? I > don't know, but once this website is back online > https://molmod.ugent.be/deltacodesdft you could check your PBE > results against Wien2K all electron calculations. Also, read: > http://arxiv.org/abs/1204.2733 > > 2) VALIDATION: is PBE or PBEsol better to describe real nickel? > I also don't know. You need to calculate properties, and see which > xc approximation matches experiments better. > > Problem 2------------ > the energy of a single atom in a unit cell (containing only that atom) > should be the same no matter where you put the atom (you are only > translating an infinite periodic system). So, the force should be > zero no matter where it is. If it's not zero, it should be very tiny, > and for reasons > like not having specified the symmetry of the system, not having converged > very well to the ground state, and because GGAs have some tiny numerical > noise. > > In your calculations, though, you use vc-relax - that doesn't make sense, > since you want the unit cell to remain large (and, for the same reason, > you do not need k-point sampling - so use gamma only sampling). > > Maybe worth looking at homework 1 and 2 and the first few lectures of: > ocw.mit.edu/3-320S05 > > > nicola > > > > > On 23/10/2014 13:17, Elliot Menkah wrote: >> Hello everyone, >> Problem 1 >> --------------------------------------- >> I'm computing for lattice constant and comparing the employment of >> exchange correlation ultra-soft pp such as LDA, PBE and PBEsol. I know >> LDA would underestimate the lattice parameter, PBE would overestimate it >> but PBEsol should do better than PBE. >> >> My calculations are shows LDA= 3.419 PBE= 3.516 PBEsol = 3.455 Angstom. >> experimnetal value I'm comparing it to is 3.522 Ang >> >> PBEsol gave a lower atomic lattice value than PBE. >> >> What could be wrong with the composition of the system? >> >> Attached is the input file(vc_ni-bulk-pbesol.in) for the PBEsol USPP >> calculations. >> >> Problem 2 >> ------------------------------------------- >> Trying to find Cohesive energy and I already have my energy of the bulk. >> I'm now computing for the energy of a single atom in a vacuum system. >> >> I added 15 15 15 Ang to the XYZ Cell parameters and the single atom sits >> in a corner whiles I expect it to sit some where in the middle. >> >> What I'm I not doing right please. >> >> Attached is the respective (evac-ni.in) file too. >> Thank you. >> >> >> >> >> Kind Regards, >> >> >> >> Elliot >> >> -- >> Elliot S. Menkah >> Research Student - Computational Chemistry/ Computational Material Science >> Theoretical and Computational Chemistry >> Dept. of Chemistry >> Kwame Nkrumah UNiversity of Sci. and Tech. >> Kumasi >> Ghana >> >> Tel: +233 243-055-717 >> >> Alt Email:[email protected] >> [email protected] >> >> >> >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum >> -- Elliot S. Menkah Research Student - Computational Chemistry/ Computational Material Science Theoretical and Computational Chemistry Dept. of Chemistry Kwame Nkrumah UNiversity of Sci. and Tech. Kumasi Ghana Tel: +233 243-055-717 Alt Email: [email protected] [email protected] _______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
