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

[Peter Blaha]

ad 1) Only with force convergence, the scripts will change "TOT" to "FOR" in lapw2 and
calculate the Pulay-forces. Thus, only the "total force" is ok, while when it says
"partial forces" in the scf file, these forces are NOT complete.

ad 2) Just accept the struct-file from nn and continue. The initialization analyses the symmetry
and modifies the struct file.

> 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)
> ******************************************************
> 
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                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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