[DFTB-Plus-User] Failed geometry optimisation for 5 Au atom cluster

[Benjamin Hourahine]

Hello,

I'm a little confused why you are using DFTB+U (the OrbitalPotentials block) for gold clusters, 
what is the reason to do this? This correction is usually of use for open shell d and f elements.
Gold has a filled d-shell, and you have added the correction to the s and p shells as well.

OrbitalResolvedSCC = Yes

is probably more useful for you, and is doing something physically very different. OrbitalPotentials
add terms which are related to correcting the on-site part of the self-interaction error, while
OrbitalResolvedSCC uses a more realistic model of charge transfer between shells.

Regards

Ben
________________________________________
From: dftb-plus-user-bounces at dftb-plus.info [dftb-plus-user-bounces at dftb-plus.info] On Behalf Of Tiem Leong Yoon [tlyoon at gmail.com]
Sent: 10 May 2011 04:11
To: dftb-plus-user at dftb-plus.info
Cc: thong leng lim
Subject: [DFTB-Plus-User] Failed geometry optimisation for 5 Au atom cluster

We have constructed a Slater-Koster file for gold(Au) nanocluster and run on dftb+. The Slater- Koster information is the courtesy of Prof. Koskinen, author of the paper "Density-functional based tigh-binding study of small gold cluster, P. Koskinen et al 2006, New J. Phys. 8, 9.

We found that geometry optimization converged for 5 atoms of gold but when run with 6 atoms, the geometry would not converge even after 10000 geometry step.

For your information, the "OrbitalPotential" already added in the input file and those values are the suggestion from Prof. Koskinen.

Anything we might have overlooked in the input file?

Below is the input file.


Geometry = GenFormat {
6   C
Au
1    1     3.0         0.0      0.0
2    1     -3.0        0.0      0.0
3    1     0.0         3.0      0.0
4    1     0.0        -3.0      0.0
5    1     0.01       0.02    3.0
6    1     0.03       0.02   -3.01
}

Driver = ConjugateGradient {
  MovedAtoms = Range { 1 6 }
  MaxForceComponent = 1.0e-4
  MaxSteps = 10000
  OutputPrefix = "geom.out"
  Constraints = {}
}

Hamiltonian = DFTB {
  SCC = Yes
  SCCTolerance = 1.0e-5
  MaxSCCIterations = 1000
  Mixer = Broyden {
    MixingParameter = 0.2
  }
  SlaterKosterFiles = {
    Au-Au = "Au-Au.skf"
  }
  MaxAngularMomentum = {
    Au = "d"
  }
  Charge = 0.0
  SpinPolarisation = {}
  Filling = Fermi {
    Temperature [Kelvin] = 0.0
  }

Eigensolver = RelativelyRobust {}
OrbitalPotential = FLL {
 Implementation = "on-site"
 LConstants = {
  Au = {0.25 0.25 0.25 }
  }
}
}


Options = {}
ParserOptions = {
  ParserVersion = 3
}