[Pw_forum] Rh2 Dimer Bond Length.

[Paolo Giannozzi]

I think that the problem is that if you push 
pseudopotentials with nonlinear core correction 
(the "-n-" letter in the pseudopotential name) 
so close that they overlap, unpredictable 
results may follow

P.

On Fri, 2014-02-21 at 11:52 +0000, 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
> 
> 
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://pwscf.org/mailman/listinfo/pw_forum

-- 
 Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
 Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
 Phone +39-0432-558216, fax +39-0432-558222