Re: about LDA band gap of bulk Si ( No.1 ) 
 Date: 2005/04/07 18:02
 Name: T.Ozaki
 Thank you for your report.
I have found that the overestimated band gap is due to the lack of the nonlocal part for the dstate in Si_TM.vps. It seems that Si_TM.vps does not provide an appropriate potential to the conduction band for which the dstate contributes. To improve it, new relativistic pseudo potentials (Si_LDA.vps, Si_GGA.vps) and new basis functions have been generated including the dstates which are downloadable from http://staff.aist.go.jp/tozaki/vps_pao/Si/index.html
The revised pseudo potential well reproduces a previously reported LDA gap of bulk Si as well as the lattice constant (see the above web). Please try the calculations using the pseudo potentials. As for the basis set, Si7.0R and Si7.5R seem to be close to an overcomplete basis set, maybe the best choice for the basis set is Si6.0Rs2p2d1 or Si6.5Rs2p2d1.
> By the way, does the origin(0.0ev) fo the energy in both DOS calculation and BAND > dispersion correspond to the Fermi energy ?
You are right.
The following is just a remark. When a unexpected band gap is obtained, there would be two reasons:
(1) less accurate basis set A less accurate basis set (short cutoff and small number of basis functions) overestimates eigenvalues of the conduction band, since the conduction band usually more extends and more oscillates than the valence band in real space.
(2) less accurate pseudo potential When the lower excited states are crucial to determine the band gap, it is desirable to include the first excited state (polarization state) in the generation of pseudo potential. The Si pseudo potential was the case. Since the dstate is not included in the pseudo potential generation for the other elements (P, S, Cl, Ge, As, Se, Br), I wonder that the band gap of materials consisting of these elements is less reproduced. If someone reports any flaw in pseudo potentials of these elements, I would appreciate the cooperations.
Regards,
T. Ozaki

Re: about LDA band gap of bulk Si ( No.2 ) 
 Date: 2005/04/10 12:21
 Name: Brighton Yan
The same trouble has also been found for Ge case. It seems that those pseudopotentials and PAOs should be revised.

