Re: [Pw_forum] Band gap value through charged supercell calculation
Dear Evan, I would consult literature for that matter. It is very difficult and counterproductive to discuss this in an online forum. Mostafa ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
Re: [Pw_forum] Band gap value through charged supercell calculation
Dear Layla and Mostafa For calculating the energy of the charged defects, when setting the variable tot_charge, a compensating jellium background is automatically inserted to remove divergences (dealing with the Columbic interactions between the defects) In a periodic calculation (mentioned in the document), therefore, is it still necessary to set the assume_isolated (like makov-payne) in the supercell calculations. I am not familiar with the defect calculation, what are the functions for makov-payne corrections. Any comments are appreciated. Regards Evan USC, China 在2016-05-27，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27日 星期五 收件人: "pw_forum@pwscf.org" <pw_forum@pwscf.org> 主题: Re: [Pw_forum] Band gap value through charged supercell calculation Correction: I-A= E(N+1)+E(N-1)-2E(N) Mostafa ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
Re: [Pw_forum] Band gap value through charged supercell calculation
Correction: I-A= E(N+1)+E(N-1)-2E(N) Mostafa ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
Re: [Pw_forum] Band gap value through charged supercell calculation
Dear Evan and Layla, E(N+x) where x is a real number can be calculated using tot_charge: http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#idm6396048 The ionization potential is not well-defined in bulk as Layla described but the difference I-A is well-defined for bulk. I-A= E(N+1)+E(N)-2E(N) Regards, Mostafa MIT ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
Re: [Pw_forum] Band gap value through charged supercell calculation
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 > ___ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum
Re: [Pw_forum] Band gap value through charged supercell calculation
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
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
