<div dir="ltr">Dear Quantum Espresso Users, Developers and Everybody in Between
<br>
<br>(Sorry for the loong e-mail, which may take time equivalent of drinking
a cup of espresso, to read)
<br>(I have tried to follow the "posting guidelines" in the Quantum Espresso
page before posting. I hope this e-mail is an appropriate one)
<br>(To make the e-mail easy to read for time-lacking people I have put $$$
in front of every question)
<br>(If I solve my problems and understand everything, I promise to take the
responsibility to reply similar questions in the forum in 2014)
<br>
<br>Thank you very much in advance.
<br>
<br>INTRO:
<br>I have a problem which results from my partial or complete lack of
understanding related to couple of points.
<br>My ultimate purpose is to calculate surface core-level shifts for couple
of elements in an insulator (I prefer to keep the material confidential)
to compare/guide to XPS measurements.
<br>I eventually want to use PAW pseudopotentials (PP) and generate my own
(with and without the core-hole on the appropriate energy level) by
using AtomPaw code. I have not used ld1.x because of two reasons.
Firstly, with my all respect to ld1.x, I personally found it a bit more
complicated for a beginner to begin with. Secondly, for AtomPaw code the
input files for well-tested PPs are very easily available so that one
can just remove one core-electron and good to go (I hoped).
<br>
<br>THE CASE STUDY 1 (Benzene Molecule):
<br>To understand the concept and warm myself up I first made some trivial
calculations with a benzene molecule using PPs generated by experts
(details are coming).
<br>When I calculate the benzene molecule with ordinary PPs, in the output
file I get number of electrons as 30. This number makes sense: 6 carbon
atoms each with 4 valence electrons and 6 hydrogen atoms each with 1;
add up to 30.
<br>When I replace one of the carbon PP with a corresponding PP with 1s core
hole, in the output file I get 31 electrons.
<br>The PP I use with the core-hole has the following info among others:
<br>
<br>--------------------
<br><PP_INFO>
<br>Generated using "atomic" code by A. Dal Corso (espresso distribution)
<br>Author: Paolo Giannozzi Generation date: 7Feb2008
<br>Info: C PBE with a 1s core-hole: 1s1 2s2 2p2 RRKJ3 US
<br>nl pn l occ Rcut Rcut US E pseu
<br>2S 1 0 2.00 1.40000000000 1.60000000000 -2.19814028365
<br>2S 1 0 0.00 1.40000000000 1.60000000000 0.05000000000
<br>2P 2 1 2.00 1.30000000000 1.60000000000 -1.56800948749
<br>2P 2 1 0.00 1.30000000000 1.60000000000 0.05000000000
<br>3D 3 2 -2.00 1.30000000000 1.30000000000 0.15000000000
<br><PP_HEADER>
<br>5.00000000000 Z valence
<br>Wavefunctions nl l occ
<br> 2S 0 2.00
<br> 2P 1 2.00
<br>--------------------
<br>
<br>When I run this (an SCF calculation) I get the error message saying:
<br>"charge is wrong: smearing is needed"
<br>and a bit below a warning:
<br>"WARNING: integrated charge= 30.30000000, expected= 31.00000000"
<br>When I add smearing (occupations='smearing', degauss = 0.1,
smearing='gauss') fairly calculation runs without any problem but
unfairly WARNING disappears.
<br>
<br>QUESTION SET NUMBER ONE:
<br>$$$ Is this supercell charged with and/or without smearing?
<br> $$$ If yes how the charged-supercell is taken care of (is "a
compensating jellium background is inserted" automatically without
prompting the user)?
<br>$$$ What is integrated charge and what is expected charge?
<br>$$$ Why z_valance is 5?
<br> $$$ If one puts one of the 1s core electrons into the one of the
valence levels should not this make 2p level occupied by 3 electrons
instead of 2 and write this explicitly in the PP file as 1s2 2s2 2p3?
<br>$$$ Does ld1.x calculate Z_valence as (atomic number) - (number of core
electrons) or it just counts the electrons in the valence level given by
the user?
<br>
<br>ONE COMMENT AND TWO QUESTIONS:
<br>I assume that a PP with a core electron moved to valence level can be
quite suitable for X-ray absorption process and with certain
approximations for XPS, too. But let say that I want to try the case
with 4 valence electrons and that somehow I create a PP for C atom with
a core-hole and Z_valence value of 4 and used in my trivial benzene
calculation.
<br>$$$ Would this supercell be charged?
<br> $$$ If yes how the charged-supercell is taken care of (is "a
compensating jellium background is inserted" automatically)?
<br>$$$ In general, is it possible to generate a charged-supercell with
Quantum Espresso (or any other planeweve DFT code) just with ionized PPs
or the only way is to use appropriate keyword, total_charge?
<br>
<br>CASE STUDY 2 (Generating PPs with AtomPaw) AND ONE QUESTION:
<br>As far as I understood when one creates a PP with ld1.x one need to
input atomic symbol Xor atomic number. So inputting both "C" and "6" is
not allowed.
<br>However in AtomPaw input, one has to write both C and 6 but in this case
6 represents the total number of electrons (this is what I understood
from the user manual).
<br>The AtomPaw generates a lot of output files two of which are the actual
PP files: one with an .xml extension and one with an .upf extension for
Quantum Espresso.
<br>
<br>When I generate a PP with a core-hole I assumed that total number of
electrons for C should be 5 with 1s1 2s2 2p2 configuration.
<br>In this case in the .xml file I read: "<atom symbol= "C" Z="5" core="1"
valence="4"/>" and in the corresponding .upf file in the <PP_HEADER> I
read z_valence = 4.
<br>
<br>When I generate a PP with a core-hole but this time with C and 6
electrons (keeping everything else the same).
<br>In the .xml file I read: "<atom symbol= "C" Z="6" core="1"
valence="5"/>" and in corresponding .upf file in the <PP_HEADER> I read
z_valence = 4.
<br>$$$ Why z_valence value is not correctly inserted into the .upf file,
i.e., always becomes 4?
<br>
<br>
<br>With my Kind regards
<br>
<br><div class=""><span class="">-- </span></div><div class=""><span class=""><br></span>Evren Ataman
<br>/University of Copenhagen/Department of Chemistry<br></div></div>