Also, the BURAI GUI gives the option to enter in either kbar or GPa. Regards,
*Chaman Gupta* Graduate Research Student, *Novosselov Research Group <http://depts.washington.edu/nrglab/>, UW* Graduate Research Student, *Pauzauskie Research Group <https://depts.washington.edu/pzlab/wordpress/>, UW* University of Washington Seattle, *M.S. in Mechanical Engineering* IIT Kharagpur, *B.Tech in Metallurgical and Materials Engineering* *Linked In <https://www.linkedin.com/in/professorchamangupta> | Email <cha...@uw.edu> | **P*: +1 (206) 383-3514 On Wed, May 20, 2020 at 5:05 AM Chaman Gupta <cha...@uw.edu> wrote: > Great explanation. That clears up so many of my questions, and the > in-general how to approach my problem. > When you say feed the final geometry, you are referring to the a,b,c and > alpha,beta,gamma values right? > > A fundamental question: > > When I say that I have a structure and I apply external pressure to it, > then I wanna see how the band structure changes. So the band structure is > basically the electronic energy levels (valence and conduction). Now apart > from the pressure changing my cell geometry, shouldn't there be an effect > of this external pressure on these energies? Or is it all accounted for > when I just change the cell geometry (a,b,c and alpha,beta,gamma) to > calculate the new band structure at a different pressure? > > Regards, > > *Chaman Gupta* > Graduate Research Student, *Novosselov Research Group > <http://depts.washington.edu/nrglab/>, UW* > Graduate Research Student, *Pauzauskie Research Group > <https://depts.washington.edu/pzlab/wordpress/>, UW* > University of Washington Seattle, *M.S. in Mechanical Engineering* > IIT Kharagpur, *B.Tech in Metallurgical and Materials Engineering* > *Linked In <https://www.linkedin.com/in/professorchamangupta> | Email > <cha...@uw.edu> | **P*: +1 (206) 383-3514 > > > On Wed, May 20, 2020 at 4:43 AM M.J. Hutcheon <mjh...@cam.ac.uk> wrote: > >> Dear Chaman, >> >> Firstly, the pressures in QE are in kbar, not GPa (I don't know if this >> is different in the GUI version), see >> https://www.quantum-espresso.org/Doc/INPUT_PW.html. Because the cell >> changes shrinks (and possibly the atoms move) as you increase the pressure, >> you should do a geometry optimisation at each new pressure, before >> calculating anything. The final geometry at each pressure can then be fed >> into further calculations, which now no longer need to know about the >> external pressure, as they only depend on the geometry (this is why the scf >> calculation will not accept a pressure). Anything that QE can calculate can >> be calculated as a function of pressure by this method. >> >> Best, >> >> Michael >> >> On 2020-05-20 12:22, Chaman Gupta wrote: >> >> Thanks a lot Michael for the explanation. Diving a bit more into my >> specific situation, here's my problem statement: >> >> I have a 'Si simple hexagonal phase (Phase V)' which is stable in the >> pressure range of 17 to 30 GPa (approx.). I want to generate the band >> structure for this Si at different Pressure values. >> *Note: My cell dimensions will vary with change in Pressure* >> >> 1. I have the cif file for this phase. Should I in this case run a >> geometry optimization and look at the HOMO LUMO energy difference to >> compute the band gap, >> or, Should I run a scf calculation and look at the HOMO LUMO energy >> difference to compute the band gap. >> >> 2. When I am running a 'scf' calculation, and I try to enter (P = 19.5 >> GPa): >> &CELL >> cell_dofree = "all" >> cell_dynamics = "bfgs" >> press = 1.95000e+02 >> press_conv_thr = 5.00000e-01 >> >> The BURAI does not take in this command when I hit update. Whilst, if I >> enter the same command while doing a geometry optimization it does update >> my input file. >> a. Can this command only be included while doing a geometry optimization >> calculation ('relax' or 'vc-relax')? >> b. Is there any way to include external pressure while doing the scf >> calculation? >> >> 3. Is it even possible to study (generate) band structures at different >> external pressures using QE? >> >> Thanks again for the help. >> >> Regards, >> >> *Chaman Gupta* >> Graduate Research Student, *Novosselov Research Group >> <http://depts.washington.edu/nrglab/>, UW* >> Graduate Research Student, *Pauzauskie Research Group >> <https://depts.washington.edu/pzlab/wordpress/>, UW* >> University of Washington Seattle, *M.S. in Mechanical Engineering* >> IIT Kharagpur, *B.Tech in Metallurgical and Materials Engineering* >> *Linked In <https://www.linkedin.com/in/professorchamangupta> | Email >> <cha...@uw.edu> | **P*: +1 (206) 383-3514 >> >> On Wed, May 20, 2020 at 4:01 AM M.J. Hutcheon <mjh...@cam.ac.uk> wrote: >> >> Dear Chaman, >> >> Essentially, a geometry optimisation moves the atoms around to reduce the >> energy of the system. The energy of the system is calculated using an scf >> calculation. The geometry optimisation is therefore a bunch of scf >> calculations strung together, with a succession of atomic positions >> approaching the minimum-energy positions. >> >> You should carry out a geometry optimisation if you suspect that your >> atoms are not in the ground state for your given parameters. >> >> Best, >> >> Michael Hutcheon >> >> TCM group, Cambridge University >> >> >> On 2020-05-20 11:37, Chaman Gupta wrote: >> >> Hey everyone, >> >> Might be a very naive question, but I have been very confused with this >> recently. >> >> I have a 'Si - simple hexagonal' cif file. I want to see the band >> structure and/or the band gap (HOMO - LUMO). >> 1. I ran a 'scf' calculation on BURAI (a GUI for QE). It generated an >> output file which gave me the Total energy and the energy of HOMO and LUMO. >> 2. Now separately, I ran a 'geometry optimization' calculation (both >> 'relax' and 'vc-relax': thus 2 different calculations), again on BURAI, and >> I got an output file, which gives me Total energy and energy of HOMO and >> LUMO. >> >> *I specified nbnd = 8 (no. of bands) for both the above mentioned >> calulations* >> >> I am confused as in which one is correct or more reliable. And also when >> should we use which calculation? >> >> Help is really appreciated. >> >> Regards, >> >> *Chaman Gupta* >> Graduate Research Student, *Novosselov Research Group >> <http://depts.washington.edu/nrglab/>, UW* >> Graduate Research Student, *Pauzauskie Research Group >> <https://depts.washington.edu/pzlab/wordpress/>, UW* >> University of Washington Seattle, *M.S. in Mechanical Engineering* >> IIT Kharagpur, *B.Tech in Metallurgical and Materials Engineering* >> *Linked In <https://www.linkedin.com/in/professorchamangupta> | Email >> <cha...@uw.edu> | **P*: +1 (206) 383-3514 >> >> _______________________________________________ >> Quantum ESPRESSO is supported by MaX (www.max-centre.eu/quantum-espresso) >> users mailing list users@lists.quantum-espresso.org >> https://lists.quantum-espresso.org/mailman/listinfo/users >> >> >> >>
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