Hi, As David said, (a,b,c) were fitted to reproduce at best the experimental band gap of 23 solids. mBJ works quite well for many other solids not included in this set, but there are also (many) cases where the mBJ band gap is relatively far from experiment (still too small, but better than LDA/GGA).
Anyway, since mBJ band gaps are much closer to experiment than LDA/GGA, then it is maybe not by luck that you got good results for your systems, but because it was designed for that. DFT would not need adjustable parameters if there was a functional/potential which always leads to sufficiently accurate results. It does not exist yet. F. Tran On Fri, 4 Mar 2016, Parker, David S. wrote:
Pablo, if you read Fabien's original 2009 PRL on the mBJ the parameters (a.b.c) were chosen to reproduce Experimental band gaps. This does not call the work into question, the basic method is on solid ground, but there is a certain empirical fitting involved. It usually does reasonably well for this precise reason. Remember it is an exchange correlation potential, not a functional like GGA. Best, David Parker Fabien, perhaps you can comment on the above. -----Original Message----- From: wien-boun...@zeus.theochem.tuwien.ac.at [mailto:wien-boun...@zeus.theochem.tuwien.ac.at] On Behalf Of delamora Sent: Friday, March 04, 2016 1:11 PM To: A Mailing list for WIEN2k users Cc: Juan Manuel Radear; gt Subject: Re: [Wien] How to get accurate GAP using BJ or mBJ methods? Dear Fabien, I think that there is a confusion here; Semi empirical methods need parameters and one get, adjusting parameters, good results On the other hand DFT, in principle, does not need adjustable parameters. There are issues that need adjustable parameters, such as the Hubbard U. My impression was that the BJ was an improvement that did not need any extra adjustable parameters, but from what you are saying, I am wrong. Is this the case? We used the mBJ for K2LnTa3O10 (1) and for Ce1/3NbO3 (2) and we got good results. Was this just good luck? Yours Pablo de la Mora 1) https://www.researchgate.net/profile/Pablo_De_La_Mora/publication/258749881_Evaluation_of_the_band-gap_of_Ruddlesden-Popper_tantalates/links/54ad94470cf24aca1c6f66c0.pdf 2 ) On the mechanism of electrical conductivity in Ce1/3NbO3, Computational Materials Science Volume 111, January 2016, Pages 101?106 ________________________________________ De: wien-boun...@zeus.theochem.tuwien.ac.at <wien-boun...@zeus.theochem.tuwien.ac.at> en nombre de t...@theochem.tuwien.ac.at <t...@theochem.tuwien.ac.at> Enviado: lunes, 29 de febrero de 2016 11:40 a. m. Para: A Mailing list for WIEN2k users Asunto: Re: [Wien] How to get accurate GAP using BJ or mBJ methods? The fundamental problem of DFT is to be an approximate method whatever is the xc functional/potential that is used. Anyway, if you really need band structure for your compounds with correct band gap, then you can empirically adjust the parameter c of the mBJ potential until the desired band gaps is obtained. For this, you need to create the file case.in0abp. For instance if you want to fix c to 1.2, the case.in0abp should be like this (see Sec. 4.5.9 of the UG): 1.2 0.0 1.0 F. Tran On Mon, 29 Feb 2016, JingQun wrote:Dear all, I am running wien 14.2 on a machine with operating system centos 6.5, fortran compiler ifort. I want to calculate the electronic structures of borates （such as BBO, KBBF, LBO, and so on）and get accurate GAP using BJ or mBJ methods. During the calculation, I have encountered some problems. They are: 1, Take KBBF for example. The bandgap of KBBF is 8.0 eV (the UV cutoff edge is about 155 nm). During the calculation, the unit-cell parameters and atomic coordinates were obtained from XRD, and the RMT were set as K (2.50), Be(1.28), B(1.19), O(1.38) F(1.56). The core electron states were separated from the valence states by -8.0 Ry, and the Rkmax was set as 5.0. The Irreducible Brillouin Zon was sampled at 500 k-points without shifted meshes, and the convergent condition for SCF was set as 10E(-5). In order to get accurate GAP as described elsewhere, a mBJ method was used. While unlike many other successful example, the bandgap obtained is either larger or smaller than the experimental values. That is to say, when I chose ‘Original mBJ values (Tran,Blaha PRL102,226401)’to calculate, the GAP of KBBF is about 11.504 eV, much larger than the experimental values (8.0 eV), while when I chose ‘Unmodified BJ potential (Becke,Johnson J.Chem.Phys 124,221101’, the result is 7.301 eV, smaller than experimental values. Can anyone kindly tell me how to get accurate bandgap value of borates ? PS: The KBBF.struct, KBBF.in1c, KBBF.in2c were added as attachment. KBBF.struct blebleble R LATTICE,NONEQUIV.ATOMS 5 155 R32 MODE OF CALC=RELA unit=bohr 8.364065 8.364065 35.454261 90.000000 90.000000120.000000 ATOM -1: X=0.00000000 Y=0.00000000 Z=0.00000000 MULT= 1 ISPLIT= 4 K NPT= 781 R0=.000050000 RMT= 2.50000 Z: 19.00000 LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000 0.0000000 1.0000000 0.0000000 0.0000000 0.0000000 1.0000000 ATOM -2: X=0.72172000 Y=0.72172000 Z=0.72172000 MULT= 2 ISPLIT= 4 -2: X=0.27828000 Y=0.27828000 Z=0.27828000 F NPT= 781 R0=.000100000 RMT= 1.56 Z: 9.00000 LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000 0.0000000 1.0000000 0.0000000 0.0000000 0.0000000 1.0000000 ATOM -3: X=0.80242000 Y=0.80242000 Z=0.80242000 MULT= 2 ISPLIT= 4 -3: X=0.19758000 Y=0.19758000 Z=0.19758000 Be NPT= 781 R0=.000100000 RMT= 1.28 Z: 4.00000 LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000 0.0000000 1.0000000 0.0000000 0.0000000 0.0000000 1.0000000 ATOM -4: X=0.50000000 Y=0.19045000 Z=0.80955000 MULT= 3 ISPLIT= 8 -4: X=0.80955000 Y=0.50000000 Z=0.19045000 -4: X=0.19045000 Y=0.80955000 Z=0.50000000 O NPT= 781 R0=.000100000 RMT= 1.38 Z: 8.00000 LOCAL ROT MATRIX: 0.0000000 0.5000000 0.8660254 0.0000000-0.8660254 0.5000000 1.0000000 0.0000000 0.0000000 ATOM -5: X=0.50000000 Y=0.50000000 Z=0.50000000 MULT= 1 ISPLIT= 4 B NPT= 781 R0=.000100000 RMT= 1.19 Z: 5.00000 LOCAL ROT MATRIX: 1.0000000 0.0000000 0.0000000 0.0000000 1.0000000 0.0000000 0.0000000 0.0000000 1.0000000 6 NUMBER OF SYMMETRY OPERATIONS -1 0 0 0.00000000 0 0-1 0.00000000 0-1 0 0.00000000 1 0-1 0 0.00000000 -1 0 0 0.00000000 0 0-1 0.00000000 2 0 0-1 0.00000000 0-1 0 0.00000000 -1 0 0 0.00000000 3 0 1 0 0.00000000 0 0 1 0.00000000 1 0 0 0.00000000 4 0 0 1 0.00000000 1 0 0 0.00000000 0 1 0 0.00000000 5 1 0 0 0.00000000 0 1 0 0.00000000 0 0 1 0.00000000 6 KBBF.in1c WFFIL EF=-.100583812400 (WFFIL, WFPRI, ENFIL, SUPWF) 5.00 10 4 (R-MT*K-MAX; MAX L IN WF, V-NMT 0.30 4 0 (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW) 0 -2.30 0.002 CONT 1 0 0.30 0.000 CONT 1 1 -1.08 0.002 CONT 1 1 0.30 0.000 CONT 1 0.30 3 0 (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW) 0 -1.90 0.002 CONT 1 0 0.30 0.000 CONT 1 1 0.30 0.000 CONT 1 0.30 2 0 (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW) 0 0.30 0.000 CONT 1 0 -7.51 0.001 STOP 1 0.30 3 0 (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW) 0 -1.46 0.002 CONT 1 0 0.30 0.000 CONT 1 1 0.30 0.000 CONT 1 0.30 2 0 (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW) 0 0.30 0.000 CONT 1 1 0.30 0.000 CONT 1 K-VECTORS FROM UNIT:4 -11.0 1.5 54 emin / de (emax=Ef+de) / nband KBBF.in2c TOT (TOT,FOR,QTL,EFG,FERMI) -14.00 52.00 0.50 0.05 1 EMIN, NE, ESEPERMIN, ESEPER0, iqtlsave TETRA 0.000 (GAUSS,ROOT,TEMP,TETRA,ALL eval) 0 0 2 0 -3 3 4 0 4 3 -5 3 6 0 6 3 6 6 0 0 1 0 2 0 3 0 3 3 -3 3 4 0 4 3 -4 3 5 0 5 3 -5 3 6 0 6 3 -6 3 6 6 -6 6 0 0 1 0 2 0 3 0 3 3 -3 3 4 0 4 3 -4 3 5 0 5 3 -5 3 6 0 6 3 -6 3 6 6 -6 6 0 0 1 0 2 0 2 2 -2 2 3 0 3 2 -3 2 4 0 4 2 -4 2 4 4 -4 4 5 0 5 2 -5 2 5 4 -5 4 6 0 6 2 -6 2 6 4 -6 4 6 6 -6 6 0 0 2 0 -3 3 4 0 4 3 -5 3 6 0 6 3 6 6 14.00 GMAX NOFILE FILE/NOFILE write recprlist 2, In some papers, they said ‘The potential and charge density in the muffin-tin (MT) spheres are expanded in spherical harmonics with lmax = 8 and non-spherical components up to lmax = 6.’I don’t know how to set different lmax value during the calculation. Can anyone tell me how to do ? Thanks very much. Yours Qun Jing_______________________________________________ Wien mailing list Wien@zeus.theochem.tuwien.ac.at http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien SEARCH the MAILING-LIST at: http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
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