Vibrational analysis for single atom

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I'm trying to do some vibrational analyses to calculate free energies of some bond dissociation reactions. When I do some single atom anions however (Cl-, Br-), I get the following error:

  You want to calculate the vibrational frequencies for            1  atoms?
  Unfortunately this is not possible
 vib_vib: bomb      911
 There is an error in the input file
 For more information see the NWChem manual at

 For further details see manual section:                                                                                                                                            
0:vib_vib: bomb:Received an Error in Communication
application called MPI_Abort(comm=0x84000000, 911) - process 0

This is the input:

start job

title "Chloride anion"

 Cl                    0.00000000     0.00000000     0.00000000

charge -1

  * library 6-311G**

  xc m06-2x
  iterations 50

  temp 7 273.15 298.15 323.15 373.15 423.15 453.15 473.15

task dft energy
task dft freq

Am I doing something wrong or is this simply not possible?

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Nuclear displacements
I am not quite sure anybody has figured out yet how to calculate the nuclear displacements of a single atom.

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I understand that the vibrational analysis itself cannot be done in a meaningful way, but it would be useful if the program still did the thermochemistry.
I managed to do it by hand now, but since I don't calculate translational entropies on a daily basis, it took me while to figure out how to do it.

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