Differences

This shows you the differences between two versions of the page.

--- howto:xas_tdp [2021/08/02 15:28] – [FAQ] abussy
+++ howto:xas_tdp [2021/08/02 15:36] – [Brief theory recap] abussy
@@ Line 516: / Line 516: @@
 $$
-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:
@@ Line 846: / Line 846: @@
 === Why is the LOCALIZE keyword required ? ===
-In order to efficiently evaluate the antisymmetric integrals of the type $\l$
+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.