XPS

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General workflow

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. It is recommended to deactivate vdW. Comment all parallelization flags to use the default:

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

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

  ICORELEVEL = 1     # State before excitation XPS.
# CLNT = 2           # species in POSCAR, second in the example.
# 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.  
  NELECT=            # Put the same number of electrons from a normal calculation. 

• After the job is completed:

 grep TOTEN OUTCAR | tail -n 1 # let's call this value E0

• In parallel, insert tags for XPS calculation to INCAR of xps1:

  ICORELEVEL = 2     # final state approximation (fss, with electron exitation).
  CLNT = 2           # species in POSCAR, second in the example.
  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.    
  NELECT=            # For fss, put an additional electron. For iss, don't.  

• After the job is completed:

 grep TOTEN OUTCAR | tail -n 1 # let's call this value E1

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

 Exps = E1 - E0

Additional information

Media:Overview.pdf (by Nathan)