[DFTB-Plus-User] Problems with Ni-Ni parameter set

[Reinaldo Pis Diez]

Dear Ashwin,

The only parameters for nickel I could found are those from the 
trans3d set. The short description accompanying that set states that 
it was developed to simulate biological systems. Thus, I guess that 
parameters for nickel should reproduce well some results for Ni(II) 
within bio-inorganic systems.
In other words, it is not strange that you are unable to find the 
expected lattice constant for bulk nickel.
Regards,

Reinaldo

On 12/07/2010 03:09 PM, Ashwin Ramasubramaniam wrote:
> Hello,
>
> I seem to be having trouble getting the Ni-Ni parameter set to
> correctly reproduce the bulk Ni fcc structure with the trans3d
> parameter set. I try to generate an energy vs. lattice parameter curve
> using the script below:
>
> =========
> #! /bin/bash
>
> for a in 3.49 3.50 3.51 3.52 3.53 3.54 3.55 3.56 3.57 3.58 3.59 3.60
> do
>
> b=$(echo "$a/2"|bc -l)
>
> cat>dftb_in.hsd<<!
> Geometry = {
>    Periodic = Yes
>    LatticeVectors [Angstrom] = {
>      $b $b 0.0
>      $b 0.0 $b
>      0.0  $b $b
>    }
>   TypeNames = { "Ni" }
>   TypesAndCoordinates [relative] = {
>     1  0.00  0.00  0.00
>   }
> }
>
> Hamiltonian = DFTB {
>    SCC = Yes
>    SCCTolerance = 1e-5
>    MaxAngularMomentum = {
>      Ni = "d"
>    }
>    SlaterKosterFiles = Type2FileNames {
>      Prefix = ""
>      Separator = "-"
>      Suffix = ".skf"
>    }
>    KPointsAndWeights = SupercellFolding {
>      21  0   0
>      0   21  0
>      0   0   21
>      0.0 0.0 0.0
>    }
>
>    SpinPolarisation = NonColinear {
>      InitialSpins = {
>        AtomSpin = {
>          Atoms = 1:-1
>          SpinPerAtom = 0.0 0.0 1.0
>        }
>      }
>    }
>    SpinConstants = {
>      Ni = {
>      # Wss Wsp Wsd Wps Wpp Wpd Wds Wdp Wdd
>      -0.016 -0.012 -0.003 -0.012 -0.022 -0.001 -0.003 -0.001 -0.018
>      }
>    }
>    Filling = MethfesselPaxton {
>      Temperature [K] = 0.0
>      Order = 2
>    }
> }
> !
>
> dftb+
>
> echo $a>>  SUMMARY
> grep Mermin detailed.out>>  SUMMARY
>
> done
> ============
>
> The resulting output looks like this:
>
> 3.49
>   Total Mermin free energy:          -1.9957949329 H          -54.3083 eV
> 3.50
>   Total Mermin free energy:          -1.9991749718 H          -54.4003 eV
> 3.51
>   Total Mermin free energy:          -2.0024539886 H          -54.4895 eV
> 3.52
>   Total Mermin free energy:          -2.0055871453 H          -54.5748 eV
> 3.53
>   Total Mermin free energy:          -2.0085331500 H          -54.6550 eV
> 3.54
>   Total Mermin free energy:          -2.0112561646 H          -54.7291 eV
> 3.55
>   Total Mermin free energy:          -2.0137270004 H          -54.7963 eV
> 3.56
>   Total Mermin free energy:          -2.0159245062 H          -54.8561 eV
> 3.57
>   Total Mermin free energy:          -2.0178337657 H          -54.9081 eV
> 3.58
>   Total Mermin free energy:          -2.0194447286 H          -54.9519 eV
> 3.59
>   Total Mermin free energy:          -2.0207743557 H          -54.9881 eV
> 3.60
>   Total Mermin free energy:          -2.0218200760 H          -55.0165 eV
>
>
> The bulk lattice parameter for fcc-Ni is about 3.52 A... clearly, the
> energy is still decreasing monotonically at 3.60 A. Am I doing
> something trivially wrong here or were the Slater-Koster parameters
> not fit to the bulk fcc phase?
>
> thanks,
> -Ashwin.
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