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 (link to gli script to be added).

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

• Copy the files corresponding to your typical setup to "xps0"

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

   ISPIN = 2          # Always put this flag. 
   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

• Copy the job files from "xps0" to "xps1"

• Replace tags for XPS calculation with:

   ISPIN = 2          # Always put this flag. 
   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)