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howto:xas_tdp [2021/08/02 15:36] – [Brief theory recap] abussyhowto:xas_tdp [2021/08/02 15:40] – [FAQ] abussy
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 The only difference between the above input file and that of a standard XAS LR-TDDFT calculation is the addition of the ''&GW2X'' subsection. In this case, only default parameters are used, which corresponds to the original GW2X scheme with a convergence threshold of 0.01 eV. Note that the core specific all-electron aug-pcX-2 basis set is used (triple zeta quality). This inputs corresponds to an entry of table II in the [[https://doi.org/10.1063/5.0058124|reference paper]], although slacker parameters are used here (in order to make this tutorial cheap and easy to run, this particular calculations takes ~2 minutes on 4 cores). The only difference between the above input file and that of a standard XAS LR-TDDFT calculation is the addition of the ''&GW2X'' subsection. In this case, only default parameters are used, which corresponds to the original GW2X scheme with a convergence threshold of 0.01 eV. Note that the core specific all-electron aug-pcX-2 basis set is used (triple zeta quality). This inputs corresponds to an entry of table II in the [[https://doi.org/10.1063/5.0058124|reference paper]], although slacker parameters are used here (in order to make this tutorial cheap and easy to run, this particular calculations takes ~2 minutes on 4 cores).
  
-In the output file, the correction for each S $2p$ is displayed. Note that the correction amounts to a shift of 1.9 eV compared to standard XAS LR-TDDFT, leading to a first singlet excitation energy of 164.4 eV (at the L$_3$ edge). This fits [[https://doi.org/10.1016/s0301-0104(97)00111-0|experimental results]] within 0.1 eV. thus clearly improving the XAS LR-TDDFT result. Note that the core IPs, including spin-orbit coupling effects, are also provided. These can be directly used to produce a XPS spectrum. The content of the OCS.spectrum yields the corrected spectrum directly.+In the output file, the correction for each S $2p$ is displayed. Note that the correction amounts to a shift of 1.9 eV compared to standard XAS LR-TDDFT, leading to a first singlet excitation energy of 164.4 eV (at the L$_3$ edge). This fits [[https://doi.org/10.1016/s0301-0104(97)00111-0|experimental results]] within 0.1 eV. thus clearly improving the XAS LR-TDDFT result. Note that the core IPs, including spin-orbit coupling effects, are also provided. These can be directly used to produce a XPS spectrum. The content of the ''OCS.spectrum'' file yields the corrected spectrum directly.
  
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 === Why is the LOCALIZE keyword required ? === === Why is the LOCALIZE keyword required ? ===
-In order to efficiently evaluate the antisymmetric integrals of the type $\langle Ia | jk \rangle$, the same local RI scheme as XAS_TDP is used. Therefore, the core state $I$ needs to be local in space. However, the rotation required to get the pseudocanonical orbitals needed for the original GW2X scheme may break this localization, provided that there are other equivalent atoms in the system. To prevent that from happening, all core states localized on other atoms are ignored for the rotation and the subsequent IP calculation. This has negligible impact since core states belonging to different atoms only weakly interact. It is however important to keep the value of the LOCALIZE keyword to a minimum to insure that only core states are ignored.+In order to efficiently evaluate the antisymmetric integrals of the type $\langle Ia || jk \rangle$, the same local RI scheme as XAS_TDP is used. Therefore, the core state $I$ needs to be local in space. However, the rotation required to get the pseudocanonical orbitals needed for the original GW2X scheme may break this localization, provided that there are other equivalent atoms in the system. To prevent that from happening, all core states localized on other atoms are ignored for the rotation and the subsequent IP calculation. This has negligible impact since core states belonging to different atoms only weakly interact. It is however important to keep the value of the LOCALIZE keyword to a minimum to insure that only core states are ignored.
howto/xas_tdp.txt · Last modified: 2024/02/24 10:01 by oschuett