Calculating Mg K-XANES in MgO

To learn about the XANES spectroscopy check the following link

http://ssrl.slac.stanford.edu/conferences/workshops/srxas2011/presentations/sarangi_xanes_2011.pdf

Part I Calculation of XANES for ground state structure without core hole

MgO

(NaCl structure, a=7.96 bohr; default initialization with 1000 k-points; scf-cycle)

XSPEC task:larger EMAX in MgO.in1; select in MgO.inxs: Mg-K ABS from 0-30 eV, vary broadening)

XSPEC

If you want to include states with higher energy

Edit in1

Calculate eigenvalues interactively

Calculate partial charges interactively

(specify input: atom, n and l of core state; broadening)

Calculate X-ray spectra interactively

Plot XSPEC     or     download XSPEC ASCII files for plotting with your own plotting program                                     ----MgO.in1-----------

WFFIL  EF=.2690382784   (WFFIL, WFPRI, ENFIL, SUPWF)
  7.00       10    4 (R-MT*K-MAX; MAX L IN WF, V-NMT
  0.30    4  0      (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW)
 0    0.30      0.000 CONT 1
 0   -5.57      0.001 STOP 1
 1    0.30      0.000 CONT 1
 1   -3.12      0.001 STOP 1
  0.30    3  0      (GLOBAL E-PARAMETER WITH n OTHER CHOICES, global APW/LAPW)
 0   -1.55      0.002 CONT 1
 0    0.30      0.000 CONT 1
 1    0.30      0.000 CONT 1
K-VECTORS FROM UNIT:4   -9.0       5    18   emin / de (emax=Ef+de) / nband
-------------------------------------------------------------------

-----------------MgO-inxs-----------------------
Title: Atom 1 L3 absorption spectrum
1               (atom)
1               (n core)
0               (l core)
0,0.5,0.5       (split, Int1, Int2)
0,0.02,30      (EMIN,DE,EMAX)
ABS             (type of spectrum)
1.00            (S)
2.0            (gamma0)
1.50            (W only for EMIS)
AUTO               (AUTO or MANually select Energy ranges for broadening)
-6.93  
-10.16  
-13.9
--------------------------------------------------------

We will get the following graph

Part II Calculation of XANES for new structure with core hole

Supercells: MgO 2x2x2 FCC-supercell for core-hole simulation

create new “session”, copy MgO.struct into new directory

x supercell;(specify proper struct-filename, 2x2x2, F-lattice)

cp supercell-struct file to correct name “case.struct”; “label” 1st atom (Mg Mg1)

init_lapw

(with 200k, RKmax=6.5)

edit case.inc (remove a core electron from 1st atom)

edit case.in2 (add one valence electron)

run_lapw

(for bigger calc. use -it and compare timings for 1st and later iterations!)

edit case.in2 (remove extra valence electron)

XSPEC task for Mg-K XAS (see above)

wadha@linux-57qi:~/WIEN2k/MgO-core-hole> x supercell
 Program generates supercell from a WIEN struct file.

 Filename of struct file:
MgO-core-hole.struct

 Number of cells in x direction:
2
 Number of cells in y direction:
2
 Number of cells in z direction:
2
 Optional shift all atoms by the same amount (fractional coordinates).
 Please enter x shift:
0
 Please enter y shift:
0
 Please enter z shift:
0

 Current structure has lattice type F  
 Enter your target lattice type: (P,B,F)
f
 Target lattice type will be F  

 Supercell generated sucessfully.
 Stored in struct file: MgO-core-hole_super.struct                             
              
 You may need to replace an atom by an impurity or distort the positions, ....
0.002u 0.009s 0:50.96 0.0%      0+0k 1680+32io 6pf+0w
wadha@linux-57qi:~/WIEN2k/MgO-core-hole> cp MgO-core-hole_super.struct MgO-core-hole.struct

Edit Mg ------> Mg1

MgO                                                                            
F   LATTICE,NONEQUIV. ATOMS 16    
MODE OF CALC=RELA unit=bohr
 15.920000 15.920000 15.920000 90.000000 90.000000 90.000000
ATOM   1: X=0.00000000 Y=0.00000000 Z=0.00000000
          MULT= 1          ISPLIT= 8
Mg1        NPT=  781  R0=0.00010000 RMT=    1.9800   Z: 12.0
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                     0.0000000 1.0000000 0.0000000
                     0.0000000 0.0000000 1.0000000
ATOM   2: X=0.50000000 Y=0.00000000 Z=0.00000000
          MULT= 1          ISPLIT= 8
Mg         NPT=  781  R0=0.00010000 RMT=    1.9800   Z: 12.0
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
            

wadha@linux-57qi:~/WIEN2k/MgO-core-hole> init_lapw -b -numk 200 -rkmax 6.5

wadha@linux-57qi:~/WIEN2k/MgO-core-hole> kwrite MgO-core-hole.inc

We will adopt another way as it is mentionned in the following link

https://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/msg11037.html 


edit MgO-core-hole.inc (remove a core electron from 1st atom)   2 ----> 1

------------MgO-core-hole.inc-------------------------

 1 0.00  0  NUMBER OF ORBITALS (EXCLUDING SPIN), SHIFT, IPRINT
1,-1,1               ( N,KAPPA,OCCUP)
 1 0.00  0  NUMBER OF ORBITALS (EXCLUDING SPIN), SHIFT, IPRINT
1,-1,2               ( N,KAPPA,OCCUP)
 1 0.00  0  NUMBER OF ORBITALS (EXCLUDING SPIN), SHIFT, IPRINT
1,-1,2               ( N,KAPPA,OCCUP)
 1 0.00  0  NUMBER OF ORBITALS (EXCLUDING SPIN), SHIFT, IPRINT
1,-1,2               ( N,KAPPA,OCCUP)
 1 0.00  0  NUMBER OF ORBITALS (EXCLUDING SPIN), SHIFT, IPRINT
1,-1,2               ( N,KAPPA,OCCUP)
 0
-----------------------------------------------------------------

wadha@linux-57qi:~/WIEN2k/MgO-core-hole> kwrite MgO-core-hole.in2

edit case.inm (add a background elctron charge)
0.0  --------> 0.1

-------------------MgO-core-hole.inm---------------

 MSR1   1.0   YES  (BROYD/PRATT, BG charge (-1 for core hole), norm)
0.20            mixing FACTOR for BROYD/PRATT scheme
1.00  1.00      PW and CLM-scaling factors
9999  8        idum, HISTORY

  ---------------------------------------

wadha@linux-57qi:~/WIEN2k/MgO-core-hole> run_lapw

Now we remove again the extra elctron charge from the case.inm file

    ----------------MgO-core-hole.inm ----------

MSR1   0.0   YES  (BROYD/PRATT, BG charge (-1 for core hole), norm)
0.20            mixing FACTOR for BROYD/PRATT scheme
1.00  1.00      PW and CLM-scaling factors
9999  8        idum, HISTORY
   --------------------------------------------------------

Now from the GUI interface w2web we do XPEC calculation

XSPEC

If you want to include states with higher energy

Edit in1

Calculate eigenvalues interactively

Calculate partial charges interactively

(specify input: atom, n and l of core state; broadening)

Calculate X-ray spectra interactively

Plot XSPEC     or     download XSPEC ASCII files for plotting with your own plotting program

 ----------MgO-core-hole.inxs-----------------------

Title: Atom 1 L3 absorption spectrum
1               (atom)
1               (n core)
0               (l core)
0,0.5,0.5       (split, Int1, Int2)
0,0.02,30      (EMIN,DE,EMAX)
ABS             (type of spectrum)
1.00            (S)
2.0            (gamma0)
1.50            (W only for EMIS)
AUTO               (AUTO or MANually select Energy ranges for broadening)
-6.93  
-10.16  
-13.9

-----------------------------------------------------
We will get the following graph