rather meaningful, perhaps by chance...:-) I can only suppose part of the reason: the screening of core holes in molecules is strongly affected by electronic correlation problems, more than in the case of semiconductors or insulators. For example, if you try to estimate XPS lines of molecules by using GGA and a full core hole tecnique you find horribly large differences with respect to measurements. I've found instead errors as large as 0.1 eV on XPS lines by using B3LYP and full core holes. I've obtained some interesting density plots of the above screening in pyrimidines, which have been published here.
J. Phys. Chem. A 2009, 113, 13593?13600 In this case, nothing is "empirical" in the calculation. At the same time, I've calculated quite good NEXAFS spectra by using the B3LYP charge density and a half core hole technique, as reported in the attached image. If I do not use a core hole, thus neglecting final state effects, I obtain poor spectra. It is, admittedly, a more "empirical" use of the code, not really justified. We (chemists using QE...) would like to have fully justified quantum spectroscopy tools, including also turbo_lanczos, with EXX kernels, but we rely on you... In the meanwhile, ci arrangiamo. All the best Giuseppe On Wednesday 24 October 2012 14:06:05 Matteo Calandra wrote: > Le 24/10/12 12:00, pw_forum-request at pwscf.org a ?crit : > >It is possible indeed, in the sense that the XSPECTRA code does not stop > >complaining if you perform the calculation starting from an electronic > >density calculated by using hybrid functionals (or DFT+U). But the > >XSPECTRA code has not a calculation kernel including EXX terms, as just > >pointed out > > >by Matteo Calandra. Thus: > Not exactly. In the case of DFT+U, the lanczos is performed, as it must > be, with the > U term included in the hamiltonian. So the Hamiltonian H used in > XSpectra to perform > H|psi> is the same used to generate the charge density. > This is of course what must be done. So everything is consistent with > DFT+U. > > If you take the charge density calculated with hybrids and calculate the > H|psi> > without hybrid I do not think that the result is very meaningful... > > M. -- ******************************************************** - Article premier - Les hommes naissent et demeurent libres et ?gaux en droits. Les distinctions sociales ne peuvent ?tre fond?es que sur l'utilit? commune - Article 2 - Le but de toute association politique est la conservation des droits naturels et imprescriptibles de l'homme. Ces droits sont la libert?, la propri?t?, la s?ret? et la r?sistance ? l'oppression. ******************************************************** Giuseppe Mattioli CNR - ISTITUTO DI STRUTTURA DELLA MATERIA v. Salaria Km 29,300 - C.P. 10 I 00015 - Monterotondo Stazione (RM) Tel + 39 06 90672836 - Fax +39 06 90672316 E-mail: <giuseppe.mattioli at ism.cnr.it> -------------- next part -------------- A non-text attachment was scrubbed... Name: NEXAFS-pyrimidine-Mattioli-vs-JCP133p034302.jpg Type: image/jpeg Size: 58884 bytes Desc: not available Url : http://pwscf.org/pipermail/pw_forum/attachments/20121024/a1cf7326/attachment-0001.jpg
