[Wien] Different "total force" with or without Force convergence and Supercell of hexagonal structure.

[Donghui Guo]

Dear all,

I have two questions about Wien2k calculation.
1) I have a Ni2P structure from ICSD database. After I ran SCF with the energy convergence parameter (0.0001), I got a total force about 30 mRy/a.u.for Ni atom. If I use both energy convergence parameter and force convergence parameter (1 mRy/a.u.), the total force of Ni decreased to about 3 mRy/a.u.. Meanwhile, the total energy in both calculation is nearly same. It is confused me since the structures are same in these two calculations.

2) I want to calculate the bulk Ni2P with some P site vacancy defects. First I build a Ni2P unit cell with symmetry. The space group of Ni2P is P-62m and there are 4 inequivalent atoms in one unit cell. Then I build the supercell by "x supercell" with 2x2x2. The "x supercell" program showed:
     " Current sutructure has lattice type H
       Target lattice type will by H
       Add vacuum in z-direction for surface slab [bohr]:"
I chose "0" since I am interested in bulk. Then I got the new structure with 32 atoms.
I remove one P atom randomly in W2web interface and save this 31-atoms structure with lattice type H.
The problem is when I run NN program, it showed there are too much atoms are equivalent. I cannot find out what's wrong in the supercell-making process. 

Thank you in advance and Happy New Year.  

Best regards, 
Yours, 
Donghui Guo
2009-01-07


************************************************
Donghui Guo 
Catalysis Research Center (CRC)
Hokkaido University
21-10 Kita, Sapporo 001-0021
Japan
dhguo at cat.hokudai.ac.jp
TEL: +81-11-706 9114 (office)
******************************************************