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

[Ashwin Ramasubramaniam]

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.