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--- howto:xas_tdp [2021/08/02 15:35] – [FAQ] abussy
+++ howto:xas_tdp [2021/08/02 15:39] – [Simple examples] abussy
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-where $\varepsilon_a$ is the orbital energy of a virtual MO and $\varepsilon_I$ the energy of the donor core MO. Under Koopman's condition, these energies are interpreted as the electron affinity and and the ionization potential (IP). However, DFT is notoriously bad at prediction accurate absolute orbital eigenvalues. Therefore, and because $|\varepsilon_I| >> |\varepsilon_a|$, excitation energies are expected to be widely improved if the DFT energy $\varepsilon_I$ were to be replace by an accurate value of the IP.
+where $\varepsilon_a$ is the orbital energy of a virtual MO and $\varepsilon_I$ the energy of the donor core MO. Under Koopman's condition, these energies are interpreted as the electron affinity and and the ionization potential (IP). However, DFT is notoriously bad at predicting accurate absolute orbital eigenvalues. Therefore, and because $|\varepsilon_I| >> |\varepsilon_a|$, excitation energies are expected to be widely improved if the DFT energy $\varepsilon_I$ were to be replace by an accurate value of the IP.
 The IP can be accurately calculated using the second-order electron propagator equation:
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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).
-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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