Dear Stefano thanks for your response. Can you please guide me (1) Why vc-relax is not allowed in Q-E 5.4.0? (2) How would the band gap be effected if I relax the cell without hybrid scheme and then calculate band gap with hybrid one?
On Sat, Jul 23, 2016 at 1:07 PM, stefano de gironcoli <[email protected]> wrote: > dear Muhammad Adnan Saqlain, > > gamma extrapolation is a way to deal with the ill defined value of the > exchange integral between wfcs at k and k+q in the limit of q->0. > if you use a truncated coulomb interaction that limit is not ill > defined. > no need to use the gamma_extrapolation option > best, > stefano > > On 23/07/2016 10:00, Muhammad Adnan Saqlain wrote: > > Dear Prof Clavijo > I am extremely sorry for my misleading title of the calculation. Actually, > It was a cubic structure consisting of Cs, Pb and I. I deliberately did not > put the atoms in the calculation. more over I do not know why the algorithm > for cell movement was not copied it was however present in the input file. > > 1. If I try these two options, the > > vcut_spherical : appropriate for cubic and quasi-cubic supercells > vcut_ws : appropriate for strongly anisotropic supercells, see also > ecutvcut. > > the program says like this > > > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% > Error in routine system_checkin (1): > x_gamma_extrapolation cannot be used with vcut > > > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% > > I have no idea how to fix it. Can you suggest one?? > > 2. I have now used Q-E 5.4.0, but this version does not allow vc-relax > option with hybrid one. why is it so? How would the band gap be effected if > I relax the cell without hybrid scheme and then calculate band gap with > hybrid one? > > 3. About the ecutoff, I deliberately used small one as these are just > calculations not the real one. > 4. I have cubic system, may I try q-grid like 1*2*3 or it has to be > symmetric one? > 5. Can you suggest more about hybrid calculations? > > > On Fri, Jul 22, 2016 at 10:09 PM, Josue Itsman Clavijo Penagos < > [email protected]> wrote: > >> Dear, Muhammad Adnan Saqlain, remember the user documentation for >> *exxdiv_treatment*: >> >> Specific for EXX. It selects the kind of approach to be used >> for treating the Coulomb potential divergencies at small q vectors. >> >> gygi-baldereschi : appropriate for cubic and *quasi-cubic supercells* >> vcut_spherical : appropriate for cubic and quasi-cubic supercells >> vcut_ws : appropriate for strongly anisotropic supercells, see also >> ecutvcut. >> none : sets Coulomb potential at G,q=0 to 0.0 (required for GAU-PBE) >> >> *Besides that, *I have some observations and suggestions for you based >> in the input file you send, so you can realize why does QE is failing when >> trying to simulate your system: >> >> 1 - Check if you really need to apply smearing, since this technique is >> intended to be useful for metallic systems, and Anatase is cleary not a >> metallic system, in fact, is more a Wide-gap or Insulator -type system. >> >> 2 - You do want to perform a vc-relax calculation, but nothing are >> specified in the cards &IONS and &CELL. There is not cell relaxing >> algorithm specified (BFGS? MD?) >> >> 3 - The card &ATOMIC_POSITIONS shows nothing: No atoms, no cell to relax. >> >> 4 - In the card &SYSTEM , *ecutwfc = 40.* This, in my humble opinion, a >> very poor cutoff for a serious calculation. Do a ecutwfc convergence test >> before attempt your system. >> >> 5 - Please take in account that a hybrid calculation is VERY expensive in >> terms of computational demand, so if you set up a vc-relax calculation >> using hybrid PPS you must test if *nqx1 = 1, 2 or 3 really makes a >> difference.* >> >> *6 - For some systems, input_dft=HSE is faster than **input_dft = >> "PBE0". Check if that could be your case.* >> >> By the way, are you sure Anatase has a cubic crystal structure? Does >> XCrysden show the correct structure for your input? >> >> *Best regards, * >> >> >> Josué Clavijo, PhD. >> Assistant Professor >> Universidad Nacional de Colombia >> Departamento de Química >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > > -- > Best Regards > Muhammad Adnan Saqlain > > > > _______________________________________________ > Pw_forum mailing > [email protected]http://pwscf.org/mailman/listinfo/pw_forum > > > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum > -- Best Regards Muhammad Adnan Saqlain
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