[Pw_forum] Rh2 Dimer Bond Length.

[Hande Ustunel]

Dear Jack,

Why don't you try turning on the spin? Noble metal dimers tend to have
large magnetic moments. I recently ran a similar calculation which gave
about 2.2 A for the bond length and about 4 muB for magnetization.

Hope this helps.
Hande



On Fri, 21 Feb 2014, Jack Davis wrote:

> Dear Forum,
>
> I am trying to calculate the bond length of a rhodium dimer in Quantum ESPRESSO. However, I am gaining an unnaturally short bond length of c.a. 1.2 angstrom. I calculated this first as a relaxation, but then carried out scf steps with varying bond lengths (from about 1.0 to 3.0 angstroms) and it gave similar results. I found that this difference in energy was around 10 Ry lower than similar bond lengths. I have tried using different pseudopotentials (PBE, PBEsol and pz), reduced smearing and a higher cut off but they make little difference. I was wondering if there were any issues with my input, or if this is a result of an error in the calculation. Attached is my input file from one of the scf steps:
>
> &CONTROL
>     calculation  = "scf",
>     prefix       = "QE",
>     pseudo_dir   = "/gpfs/bb/nxf093/pseudo",
>     etot_conv_thr=  1.0D-4,
>     forc_conv_thr=  1.0D-3,
>     disk_io      = "none",
>     nstep        =  500,
> /
> &SYSTEM
>     ibrav        =  0,
>     nat          =  2,
>     ntyp         =  1,
>     ecutwfc      =  55.D0,
>     occupations  = "smearing",
>     smearing     = "fd",
>     degauss      =  0.020,
>     tot_charge     =0,
> /
> &ELECTRONS
>     electron_maxstep = 5000,
>     conv_thr     =  1.D-5,
>     mixing_beta  =  0.6D0,
>     mixing_mode  = "local-TF"
> /
> &IONS
> /
> CELL_PARAMETERS {angstrom}
> 20.00  0.00  0.00
> 0.00 20.00  0.00
> 0.00  0.00 20.00
> ATOMIC_SPECIES
> Rh  102.91  Rh.pbe-spn-kjpaw_psl.0.2.3.UPF
> ATOMIC_POSITIONS {angstrom}
> Rh   0.00000    0.00000    0.00000
> Rh   2.00000    0.00000    0.00000
> K_POINTS {Gamma}
>
> Best Wishes,
> Niall Falconbridge & Jack Davis
>
> School of Chemistry
> University of Birmingham
>
>
>

--
Hande Toffoli
Department of Physics
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Middle East Technical University
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