Hi Stefano, When I simulated for 54 atom Silicon and also for B doped Silicon(53+1), indirect bandgap was found. Though in the result, the conduction band minima is not in the correct position (i.e. not in 0.85 X, approximately in 0.65X).
For the simulation of 2 atoms, indirect bandgap is also found. The result is correct (i.e. CBM is at 0.85X) As underestimation of the bandgap value is well-known problem, it is also found in both cases. But we are more interested in direct bandgap issue now. Any suggestion regarding this will be a great help for me. Thank you very much. On Mon, Aug 1, 2016 at 11:40 AM, stefano de gironcoli <[email protected]> wrote: > Dear Mohammad, > > I suggest you do the following exercise: > Compute the band structure of 54 atom of Si with a similar setting to the > one of your present calculation. Does it have direct gap ? compute the DOS. > Compute the band structure of Silicon in the 2-atom unit cell > with celldm(1) = 10.2623467, k_points (automatic) set to 15 15 15 0 0 0 > Does it have a direct gap ? compute the DOS > Compare total energy, band structure and DOS in the two cases. > Which calculation is correct ? > > stefano > > > > On 01/08/2016 20:19, Mohammad Abu Raihan Miah wrote: > > Hi all, > > I am currently simulating band diagram for Phosphorus doped Silicon. I am > using 53 Si atoms and 1 P atom for computation. When I computed the band > diagram, it resulted in direct band gap, which is not true case for > Silicon. I have not relaxed the system. > > My input file is as follows, > > &control > calculation = 'scf', > restart_mode='from_scratch', > verbosity = 'high', > prefix = 'Silicon_P_54_relax', > tstress = .true., > tprnfor = .true., > pseudo_dir = '.', > outdir = 'out_P_rel', > wf_collect=.true., > max_seconds=10800, > / > > &system > ibrav=2, > celldm(1) = 30.787040, > nat=54, > ntyp=2, > ecutwfc=50, > ecutrho=400.0d0, > input_dft='PBE', > nbnd=120, > occupations='smearing', > degauss=0.05, > / > > &electrons > diagonalization='david', > mixing_mode = 'plain', > mixing_beta = 0.7, > conv_thr = 1.0d-6, > / > > ATOMIC_SPECIES > Si 28.085500 Si.pbe-n-rrkjus_psl.0.1.UPF > P 30.973800 P.pbe-n-rrkjus_psl.0.1.UPF > > ATOMIC_POSITIONS (alat) > Si 0.000000 0.000000 0.000000 > .................................. > P 0.083333 0.083333 0.083333 > ............................. > Si 0.750000 0.750000 0.750000 > > K_POINTS (automatic) > 5 5 5 0 0 0 > > Could anyone please explain the reason behind this change from indirect to > direct bandgap? Or any suggestion to solve this problem? > > Thank you very much. > > Best, > -- > Mohammad Abu Raihan Miah > PhD Student > Department of Electrical and Computer Engineering (ECE) > <http://www.ece.ucsd.edu/> > University of California, San Diego <http://www.ucsd.edu/> > > > _______________________________________________ > 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 > -- Mohammad Abu Raihan Miah PhD Student Department of Electrical and Computer Engineering (ECE) <http://www.ece.ucsd.edu/> University of California, San Diego <http://www.ucsd.edu/>
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