DEar Evan, you cannot get ionization energies in a bulk, unless you use a cluster of atoms to model your material (with a "welldefined" 0 energy reference).
cheers Layla 2016-05-26 18:32 GMT+02:00 毛飞 <200921220...@mail.bnu.edu.cn>: > Dear Perevalov and Mostafa, > > > > Having seen the discussions you contributed to the forum, I am more > concerned about how to calculate the ionization energy (I) of > semiconductors or insulators by pwscf codes. The definition of I=E(N-1) - > E(N), I can obtained E(N) as the ground state energy of the neutral system, > but how to get the ground state energy of positively charged system E(N). > > > > Your comments are appreciated. > > Evan > > USC, China > > 在2016-05-26，Mostafa Youssef <myous...@mit.edu> 写道: > > -----原始邮件----- > *发件人:* Mostafa Youssef <myous...@mit.edu> > *发送时间:* 2016年5月26日 星期四 > *收件人:* "pw_forum@pwscf.org" <pw_forum@pwscf.org> > *主题:* Re: [Pw_forum] Band gap value through charged supercell calculation > > > Dear Perevalov, > > > The K-S gap in left panel of Fig.2 in the paper is not what you get > directly from the occupations of the neutral cell. What is shown in the > figure is calculated using equation 13 which uses eigenvalues from the > neutral cell and occupations from charged cell. This way there will a > dependence on carrier concentration. > I believe what you plotted and found to be independent of "cell size" is > K-S gap using both eignevalues and occupations of the neutral cell. > > > You mentioned; "I understand that dependence on the supercell size is due > to compensating charge background". In fact even if you correct for the > compensating background , you will still observe dependence on the charge > density for I-A and K-S calculated with equation 13. In the dilute limit > of charged carriers you should converge to K-S gap of the neutral cell in > the case of functionals that do not have exact exchange (LDA, GGA, BYLP, > ...). For hybrid functionals that contains exact exchange (PBE0, HSE, ...) > there will be a difference between I-A and K-S (neutral) even in the > dilute limit. This is also discussed in the paper you cited right before > Fig. 2. > > It is common, at least in semiconductor defects studies , to regard I-A > as "the" band gap of the material. Some may agree , others do not. > > > For monoclinic ZrO2, the first order M-P correction was reported here: > > http://journals.aps.org/prb/abstract/10.1103/PhysRevB.75.104112 > > Of course based on the lattice parameters and supercells that the authors > reported. > > > In computing the K-S gap of a neutral cell I would use the tetrahedron > method or fixed occupations (i.e no smearing) and a dense K-point mesh > > Regards, > Mostafa Youssef > MIT > > > > > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum@pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum >
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