Re: [QE-users] Fwd: Tc for MgB2
I haven't noticed any replies to this message. I can't help with what QE does or does not do. However, there are some important points to understand about MgB2. Most of the coupling arises from 8% of the phonon BZ, and on top of that, only from 2 of the 9 phonon branches. The important Fermi surfaces are small, so k-point sampling must be very good. Then, phonon q-point sampling must be relatively high quality also. The safe way is to perform convergence tests. Warren E. Pickett Distinguished Professor of Physics Department of Physics University of California Davis Davis CA 95616, USA Cell: 530-220-2138 On Mon, Jul 9, 2018 at 12:18 AM, Mohammad Moaddeli < mohammad.moadd...@gmail.com> wrote: > > Dear all, > > I used lambda.x to calculate Tc for MgB2, as it explained in the > PHonon/.../example03, but I am confused about the results of Tc (less than > experimental reports). Input files are attached. > > Please, can somebody help me to find out the problem? > > Thanks, > > M Moaddeli, PhD > Pasargad HEI, Shiraz, Iran > > > ___ > users mailing list > users@lists.quantum-espresso.org > https://lists.quantum-espresso.org/mailman/listinfo/users > ___ users mailing list users@lists.quantum-espresso.org https://lists.quantum-espresso.org/mailman/listinfo/users
Re: [Pw_forum] projwfc partially occupied levels above Fermi level
Chris, If you look at any PDOS for a d atom octahedrally coordinated with oxygen, you will see e_g DOS mixed in the (filled) oxygen band DOS. e_g orbitals point at the oxygen and couple strongly with px,py,pz. Most of the e_g weight is pushed up above the crystal field gap, but a substantial part is mixed in with oxygen -- this is actually due to antibonding coupling. So it should be recognized that the weight (and charge) is there, but otherwise ignore it as a minor complication. And related: don't take "atomic" charges from DFT codes too seriously. That said, I do look at them a lot. Warren Warren E. Pickett Distinguished Professor of Physics Department of Physics University of California Davis Davis CA 95616, USA Cell: 530-220-2138 On Wed, Nov 22, 2017 at 11:00 PM, Christoph Wolf wrote: > Dear all, > > I have a probably silly question I cannot wrap my head around: > > a sixfold coordinated FeO6 gives me quite nice, texbtook like > crystal-field split t2g (dxz, yz, xy) and eg (z^2 x^2-y^2) orbitals after > running it through projwfc. I am having a hard time interpreting the > charges, however: > > total charge = 14.9828, p = 5.9918, pz= 1.9973, px= 1.9973, py= > 1.9973, > total charge = 14.9828, d = 6.7326, dz2= 0.4228, dxz= 1.9623, dyz= > 1.9623, dx2-y2= 0.4228, dxy= 1.9623, > > i.e. the t2g are doubly occupied but the eg have half an electron each > (~1e in total) which lies above the Ef by ~0.8 eV (i.e. much higher than > the broadening which was 0.005 Ry); Is this an "residual" electron from the > ligand field and why is it picket up by the eg orbitals? > > Thanks in advance for your help and time! > > Best regards, > Chris > > -- > Postdoctoral Researcher > Center for Quantum Nanoscience, Institute for Basic Science > Ewha Womans University, Seoul, South Korea > > > ___ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
Re: [Pw_forum] Strange Values of Tc
Isaiah, I'm not familiar with the workings of QE, but without solution of the full Eliashberg equations it must be using the Allen-Dynes equation (as most do) to obtain Tc. The basic fact is that with a standard Coulomb repulsion mu-star = 0.10-0.15, with lambda less than 0.3 or so there will be no superconductivity. The A-D equation was not fit to tiny values of Tc and no one should be interested in those results. If non-zero, they will be extremely sensitive to lambda, as you can see. [And you can get nonsensical large values! as you can see] So just accept that if lambda < 0.3 or so, any results cannot be trusted and its not an interesting el-ph superconductor. Warren Warren E. Pickett Distinguished Professor of Physics Department of Physics University of California Davis Davis CA 95616, USA Cell: 530-220-2138 On Fri, Jul 28, 2017 at 12:24 AM, Isaiah Moses wrote: > Dear everyone, > > I did an el-ph calculation of a monoclinic structure and am getting really > strange values of Tc . See the result below > lambdaomega_log T_c >0.00994 112.0480.10012314E+08 >0.0376092.3730.13380511E+10 >0.0756490.2470.39802174E+19 >0.0995989.4140.19865362E+78 >0.1101089.4630.40671597-151 >0.1145490.3290.16986711E-65 >0.1167892.3200.99512429E-51 >0.1177294.6570.29927798E-46 >0.1174497.1410.16242032E-47 >0.1161999.4420.65514785E-54 > > I'm wondering why such values. > > Any comment shall be greatly appreciated. > > Thanks, > Isaiah > > -- > Isaiah Abu Moses > Graduate Student, > Physics Department, > University of Ibadan, > Nigeria > > ___ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
