core level shift (XPS spectra) & electrostatic potential at core question

[jhegedus]

Dear All,

The calculation of core level shift is described here in the VASP manual, my question is : what is the unit of the electrostatic potential at core in the OUTCAR file ?

Other question: if E_core is the electrostatic potential at an atomic site, then why is the E_core - E_Fermi the important quantity, why do I have to correct with the Fermi energy ? In other words: if I change the Fermi energy (by changing the number of electrons or the structure) then why should I correct for that change if I want to explain XPS core level shifts ?


Kind Regards,

Jozsef

if you want to contact me directly, please use my skype : jhegedus42 [/link] [link=hyperlink url]

[admin]

the reason is that for systems with periodic 3D boundary conditions there is no way to determine the energy-zero, i.e all (K-S. level) energies are only given within a constant offset in E0 (please have eg a look at Ashcroft, Mermin,...) .
Therefore, if you compare the levels of 2 different systems (calculations), you first have to correct for these offsets of both systems to have a common energy scale; for slab calculations with sufficiently thick vacuum, one can safely assume that Evac (having reached its constant value in the vacuum) can be set to E0. This is exactly what is done by the procedure described in the handbook.

[jhegedus]

Dear Admin,

Thank you for your reply. If I understand your reply correctly as it is described here => http://cms.mpi.univie.ac.at/vasp/vasp/node145.html <= the E_fermi (according to this site) must be calculated from the vacuum using a slab calculation (using the LVTOT-tag and calculating the E_Fermi from the LOCPOT file?) So if I do 3D periodic boundary calculation I cannot calculate the core level shift ? Or for 3D calculations I can use the E_Fermi provided by the OUTCAR file (for example see the end of this reply) ? What do you suggest if I want to calculate how much the core levels shift if I change the structure of a materials from crystalline to amorphous (same box, same density, same everything, only positions differ) ? See this link for experimental results: http://maxwell.phy.bme.hu/~jhegedus/GST ... lshift.png .

What is the unit of the electrostatic potential calculated by the test charge (see example of OUTCAR file below) ? Is the test charge's shape spherical ? What determines the test charge's radii ? To which orbital(atomic level) is this charge distribution to the closest? What is alpha+bet? Is that important for the core level shift calculations ? (See below a snippet of an OUTCAR file which contains the information related to these questions, it's a system with 125 atoms, the first 19 is Ge and from 20-125 is Sb, it's an amorphous GeSb system at 600K)

Kind Regards,

Jozsef

average (electrostatic) potential at core
the test charge radii are 1.1631 1.1712
(the norm of the test charge is 1.0000)
1 -29.8869 2 -29.9194 3 -29.9386 4 -29.8796 5 -29.9040
6 -29.8571 7 -29.8631 8 -29.8212 9 -29.9571 10 -29.8085
11 -29.8036 12 -30.0752 13 -29.8432 14 -29.9569 15 -29.7942
16 -29.8606 17 -29.8385 18 -29.7054 19 -29.9405 20 -86.0141
21 -86.0581 22 -86.2219 23 -86.0479 24 -86.0797 25 -86.0663
26 -86.1073 27 -86.0149 28 -85.9860 29 -86.1883 30 -86.0070
31 -86.0723 32 -86.2351 33 -86.1603 34 -86.0434 35 -86.1303
36 -86.0189 37 -86.1636 38 -86.0726 39 -86.1122 40 -86.1408
41 -85.9382 42 -86.0690 43 -85.9997 44 -86.1384 45 -86.0045
46 -86.0143 47 -86.1200 48 -86.0409 49 -85.9818 50 -86.0468
51 -86.0784 52 -86.0327 53 -86.0329 54 -85.9329 55 -86.1731
56 -86.0897 57 -86.1104 58 -86.1099 59 -86.1639 60 -86.0807
61 -86.0632 62 -86.0772 63 -86.1266 64 -86.0522 65 -86.1879
66 -86.1378 67 -86.1095 68 -86.1447 69 -86.1681 70 -85.9833
71 -86.1091 72 -86.0333 73 -86.0737 74 -85.9710 75 -85.9892
76 -86.0892 77 -86.1261 78 -86.1217 79 -86.1252 80 -86.0386
81 -86.1277 82 -86.1012 83 -86.0880 84 -86.0453 85 -85.9731
86 -85.9897 87 -86.0532 88 -86.0695 89 -86.1187 90 -86.0840
91 -86.0048 92 -86.1436 93 -86.0982 94 -86.1301 95 -86.2546
96 -86.0984 97 -86.0179 98 -86.0157 99 -86.0225 100 -85.9966
101 -86.0361 102 -86.1265 103 -86.2242 104 -86.1372 105 -86.0554
106 -86.0072 107 -85.9878 108 -86.0085 109 -86.0220 110 -86.0629
111 -86.2000 112 -86.1474 113 -85.9604 114 -86.1202 115 -86.0630
116 -86.0154 117 -86.0704 118 -86.0587 119 -86.1081 120 -86.0713
121 -86.1102 122 -86.0932 123 -86.1491 124 -85.9574 125 -86.1407



E-fermi : 6.9865 XC(G=0): -9.6929 alpha+bet :-11.8839
add alpha+bet to get absolut eigen values


Here is the XPS experiment that I would like to model with VASP : http://maxwell.phy.bme.hu/~jhegedus/GST ... lshift.png