XPS

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General workflow

in preparation (currently just a sketch)

An XPS calculation is a single ionic step calculation, and involves the explicit computation of core levels for ONE selected atom in the POSCAR.

• For a converged structure select a single atom for which the core levels shifts will be calculated. Let us suppose that you are interested in the second Pd atom in this POSCAR:

(...)
 Pd   In     O 
 4    80    119 
(...) 

• The atom(s) for which the XPS will be calculated should be separated:

(...)
 Pd  Pd  Pd   In     O 
 1   1   2    80    119 
(...)

• Create two separate subdirectories, (for example ./xps0 and ./xps1) and copy the modified POSCAR to both.

• Create a new pseudopotential file.

• Copy the KPOINTS and INCAR files of your typical setup to "xps0" and "xps1". Dipole corrections and ionic movements must be turned off. ISPIN must be turned to 2:

  ISPIN   =  2       #
# LDIPOL  =  F  
# IDIPOL  =  3  
  IBRION  = -1  
  NSW     =  1   

• In "xps0", insert tags for XPS calculation to INCAR:

  ICORELEVEL = 0     # State before excitation XPS
# CLNT = 3           # atom type POSCAR; in this case third species in the POSCAR
# CLN  = 3           # main quantum number (3d ==> N=3) 
# CLL  = 2           # l quantum number; s=0, p=1, d=2,...  
# CLZ  = 1           # number of electrons to be displaced. Do not use 0.5.  
  NELEC=             # Put the same number of electrons from a normal calculation. 

• After the job is completed:

 grep ENTOT OUTCAR # let's call this value E0

• In parallel, insert tags for XPS calculation to INCAR of xps1. The example shows the final-state approximation (fss):

  ICORELEVEL = 2     # final state approximation (fss, with electron exitation).
# ICORELEVEL = 1     # initial state approx. (iss, without electron excitation). 
  CLNT = 3           # atom type POSCAR; in this case third species in the POSCAR. 
  CLN  = 3           # main quantum number (3d ==> N=3) 
  CLL  = 2           # l quantum number; s=0, p=1, d=2,...  
  CLZ  = 1           # number of electrons to be displaced. Do not use 0.5.    
  NELEC=             # For fss, put an additional electron. For iss, don't.  

• After the job is completed:

 grep ENTOT OUTCAR # let's call this value E1

• The XPS shift (Exps) can be calculated as:

 Exps = E1 - E0

Alternatively:

compute just ICORELEVEL=2 with one positive charge in the system, then reference the core level energy (grep 3d OUTCAR #for the example above) to vacuum energy. (will elaborate in next edit)

Media:Overview.pdf (by Nathan)