[Pw_forum] Rh2 Dimer Bond Length.

[Jack Davis]

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


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