### Re: [Wien] Photon energies in XES ...

Dear Peter, I apologize for late reply - I was travelling with a very limited access to email ... Thank you very much for your clarification. Yes, I understand now, I was really mixing 2 different concepts - the spectrum quality (profile) and the energy of the core levels. If I understand you correctly, the XES spectrum itself we calculate using the final state rule (without core hole), but energy shift we calculate using Slater transition state. And the latter "trick" has nothing to do with the spectrum itself - it just fixes the incorrect core level energies ... Just a small question: Can you (or other users/developers interested in this topic) point me to a reference where the physical ground of the "final state rule" is provided? I did multiple searches in the literature, but found no derivation of this rule - it is more stated as an "observation"... Thanks a lot again for your time and comments! Sincerely, Vlad. 2015-08-28 13:38 GMT-04:00 Peter Blaha: > You are mixing 2 concepts: > > a) Yes, the final state rule applies and thus for XES calculations you > should NOT use a core hole, but use the ground state DOS. > > b) Strictly speaking, only E-tot is a valid quantity in DFT. In > particular, the eigenvalues are in principle NOT excitation energies. > However, for delocalized states (eg. valence electrons) experience has > shown that the eigenvalues (bandstructure,DOS) can be used to interprete > experimental spectra. > This is, however, no true for localized states (core states), because > these eigenvalues are not ionization energies but are defined as the > derivative of the total energy with respect to occupation of the > corresponding state. > e_i =d E / d n_i > So one can use "Slaters transition state" approximation and make a > supercell calculation, where on one atom HALF an electron should be > removed. After scf, check the eigenvalue (with respect to EF) and you > should obtain a significantly better binding energy of this core state (and > the corresponding absolute XES transition energy. > (Typically the error of a 1s core state is reduced from eg. 10 eV to about > 1 eV. > (about XPS energies and Slaters transition state see my lecture notes of > our workshops on our web site). > > > Am 28.08.2015 um 17:19 schrieb Vladimir Timoshevskii: > >> Dear Wien2k users and developers, >> >> I am working with experimentalists and try to simulate the XES measured >> by soft x-ray detector, coupled with electron microscope. So, the >> ionization source in this setup is the electronic gun of the TEM. The >> test compound is hexagonal layered BN, which was quite well studied >> before, including the similar setup. I would greatly appreciate if you >> could share your opinion on the following 2 issues, which I am facing now: >> >> i) Is it possible, in principle, to obtain correct photon energies >> instead of shifting spectrum by hand to the EF position? I understand, >> that the position of the core level (B-1s) is sensitive to the form of >> the potential well, and the closer my potential is to the real one, the >> better is the position of the core level. I tried different >> XC-functionals, and found that actually the atomic-like Hartree-Fock >> gives the best results: the whole spectrum (B K-edge) is shifted to >> higher energies, closer to experiment, and the spectrum shape is also >> much better. However, there is still ~10eV shift, relative to the >> experimental spectrum. So, the XC-functional alone does not solve this >> problem ... >> >> ii) This is a more fundamental question, and is actually related to the >> first one. I guess, the main reason for the photon energy >> underestimation is the presence of the core hole, which shifts the >> ionized core level to lower energies. I did several test calculations of >> B-K spectrum using supercells of diffferent sizes with a core hole in B >> 1s. Indeed, by playing with fractional B 1s occupation (trying to catch >> the "transition state"), it seems to be possible to shift the whole >> spectrum to experimental position. But in this case, what about the >> "rule of the final state"? According to this rule, the hole must be >> created in the valence band (and screened out), and the core lavel must >> be filled. This is what we normally assume ... Does that mean that the >> XES calculations with hole in the core are unphysical, in spite of >> giving better photon energies? May be, the situation here, especially >> when we use TEM electronic gun for core ionization, is more >> complicated? In my opinion, the valence-core transitions are happening >> in the potential, already distorted by the presence of the core hole. Am >> I right? Then, how it agrees with the "rule of the final state"? Any >> thoughts on that would be highly appreciated! >> >> Thanks a lot in advance! >> >> Vladimir Timoshevskii >> >> >> >> ___ >> Wien mailing list >>

### Re: [Wien] Photon energies in XES ...

Dear Peter, I apologize for late reply - I was travelling with a very limited access to email ... Thank you very much for your clarification. Yes, I understand now, I was really mixing 2 different concepts - the spectrum quality (profile) and the energy of the core levels. If I understand you correctly, the XES spectrum itself we calculate using the final state rule (without core hole), but energy shift we calculate using Slater transition state. And the latter "trick" has nothing to do with the spectrum itself - it just fixes the incorrect core level energies ... Just a small question: Can you (or other users/developers interested in this topic) point me to a reference where the physical ground of the "final state rule" is provided? I did multiple searches in the literature, but found no derivation of this rule - it is more stated as an "observation"... Thanks a lot again for your time and comments! Sincerely, Vlad. 2015-08-28 13:38 GMT-04:00 Peter Blaha: > You are mixing 2 concepts: > > a) Yes, the final state rule applies and thus for XES calculations you > should NOT use a core hole, but use the ground state DOS. > > b) Strictly speaking, only E-tot is a valid quantity in DFT. In > particular, the eigenvalues are in principle NOT excitation energies. > However, for delocalized states (eg. valence electrons) experience has > shown that the eigenvalues (bandstructure,DOS) can be used to interprete > experimental spectra. > This is, however, no true for localized states (core states), because > these eigenvalues are not ionization energies but are defined as the > derivative of the total energy with respect to occupation of the > corresponding state. > e_i =d E / d n_i > So one can use "Slaters transition state" approximation and make a > supercell calculation, where on one atom HALF an electron should be > removed. After scf, check the eigenvalue (with respect to EF) and you > should obtain a significantly better binding energy of this core state (and > the corresponding absolute XES transition energy. > (Typically the error of a 1s core state is reduced from eg. 10 eV to about > 1 eV. > (about XPS energies and Slaters transition state see my lecture notes of > our workshops on our web site). > > > Am 28.08.2015 um 17:19 schrieb Vladimir Timoshevskii: > >> Dear Wien2k users and developers, >> >> I am working with experimentalists and try to simulate the XES measured >> by soft x-ray detector, coupled with electron microscope. So, the >> ionization source in this setup is the electronic gun of the TEM. The >> test compound is hexagonal layered BN, which was quite well studied >> before, including the similar setup. I would greatly appreciate if you >> could share your opinion on the following 2 issues, which I am facing now: >> >> i) Is it possible, in principle, to obtain correct photon energies >> instead of shifting spectrum by hand to the EF position? I understand, >> that the position of the core level (B-1s) is sensitive to the form of >> the potential well, and the closer my potential is to the real one, the >> better is the position of the core level. I tried different >> XC-functionals, and found that actually the atomic-like Hartree-Fock >> gives the best results: the whole spectrum (B K-edge) is shifted to >> higher energies, closer to experiment, and the spectrum shape is also >> much better. However, there is still ~10eV shift, relative to the >> experimental spectrum. So, the XC-functional alone does not solve this >> problem ... >> >> ii) This is a more fundamental question, and is actually related to the >> first one. I guess, the main reason for the photon energy >> underestimation is the presence of the core hole, which shifts the >> ionized core level to lower energies. I did several test calculations of >> B-K spectrum using supercells of diffferent sizes with a core hole in B >> 1s. Indeed, by playing with fractional B 1s occupation (trying to catch >> the "transition state"), it seems to be possible to shift the whole >> spectrum to experimental position. But in this case, what about the >> "rule of the final state"? According to this rule, the hole must be >> created in the valence band (and screened out), and the core lavel must >> be filled. This is what we normally assume ... Does that mean that the >> XES calculations with hole in the core are unphysical, in spite of >> giving better photon energies? May be, the situation here, especially >> when we use TEM electronic gun for core ionization, is more >> complicated? In my opinion, the valence-core transitions are happening >> in the potential, already distorted by the presence of the core hole. Am >> I right? Then, how it agrees with the "rule of the final state"? Any >> thoughts on that would be highly appreciated! >> >> Thanks a lot in advance! >> >> Vladimir Timoshevskii >> >> >> >> ___ >> Wien mailing list >>

### Re: [Wien] Photon energies in XES ...

You are mixing 2 concepts: a) Yes, the final state rule applies and thus for XES calculations you should NOT use a core hole, but use the ground state DOS. b) Strictly speaking, only E-tot is a valid quantity in DFT. In particular, the eigenvalues are in principle NOT excitation energies. However, for delocalized states (eg. valence electrons) experience has shown that the eigenvalues (bandstructure,DOS) can be used to interprete experimental spectra. This is, however, no true for localized states (core states), because these eigenvalues are not ionization energies but are defined as the derivative of the total energy with respect to occupation of the corresponding state. e_i =d E / d n_i So one can use Slaters transition state approximation and make a supercell calculation, where on one atom HALF an electron should be removed. After scf, check the eigenvalue (with respect to EF) and you should obtain a significantly better binding energy of this core state (and the corresponding absolute XES transition energy. (Typically the error of a 1s core state is reduced from eg. 10 eV to about 1 eV. (about XPS energies and Slaters transition state see my lecture notes of our workshops on our web site). Am 28.08.2015 um 17:19 schrieb Vladimir Timoshevskii: Dear Wien2k users and developers, I am working with experimentalists and try to simulate the XES measured by soft x-ray detector, coupled with electron microscope. So, the ionization source in this setup is the electronic gun of the TEM. The test compound is hexagonal layered BN, which was quite well studied before, including the similar setup. I would greatly appreciate if you could share your opinion on the following 2 issues, which I am facing now: i) Is it possible, in principle, to obtain correct photon energies instead of shifting spectrum by hand to the EF position? I understand, that the position of the core level (B-1s) is sensitive to the form of the potential well, and the closer my potential is to the real one, the better is the position of the core level. I tried different XC-functionals, and found that actually the atomic-like Hartree-Fock gives the best results: the whole spectrum (B K-edge) is shifted to higher energies, closer to experiment, and the spectrum shape is also much better. However, there is still ~10eV shift, relative to the experimental spectrum. So, the XC-functional alone does not solve this problem ... ii) This is a more fundamental question, and is actually related to the first one. I guess, the main reason for the photon energy underestimation is the presence of the core hole, which shifts the ionized core level to lower energies. I did several test calculations of B-K spectrum using supercells of diffferent sizes with a core hole in B 1s. Indeed, by playing with fractional B 1s occupation (trying to catch the transition state), it seems to be possible to shift the whole spectrum to experimental position. But in this case, what about the rule of the final state? According to this rule, the hole must be created in the valence band (and screened out), and the core lavel must be filled. This is what we normally assume ... Does that mean that the XES calculations with hole in the core are unphysical, in spite of giving better photon energies? May be, the situation here, especially when we use TEM electronic gun for core ionization, is more complicated? In my opinion, the valence-core transitions are happening in the potential, already distorted by the presence of the core hole. Am I right? Then, how it agrees with the rule of the final state? Any thoughts on that would be highly appreciated! Thanks a lot in advance! Vladimir Timoshevskii ___ 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 -- Peter Blaha Inst.Materials Chemistry TU Vienna Getreidemarkt 9 A-1060 Vienna Austria +43-1-5880115671 ___ 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