Helium dimer dissociation curve

#!/usr/bin/env plams
import numpy as np

# Calcualte bond energy of He dimers for a series of bond
# distances using ADF

# type of atoms
atom1 = "He"
atom2 = "He"

# interatomic distance values
dmin = 2.2
dmax = 4.2
step = 0.2

# create a list with interatomic distances
distances = np.arange(dmin, dmax, step)

# calculation parameters (single point, TZP/PBE+GrimmeD3)
sett = Settings()
sett.input.ams.task = "SinglePoint"
sett.input.adf.basis.type = "TZP"
sett.input.adf.xc.gga = "PBE"
sett.input.adf.xc.dispersion = "Grimme3"

energies = []
for d in distances:
    mol = Molecule()
    mol.add_atom(Atom(symbol=atom1, coords=(0.0, 0.0, 0.0)))
    mol.add_atom(Atom(symbol=atom2, coords=(d, 0.0, 0.0)))
    job = AMSJob(molecule=mol, settings=sett, name=f"dist_{d:.2f}")
    job.run()
    energies.append(job.results.get_energy(unit="kcal/mol"))

# print
print("== Results ==")
print("d[A]    E[kcal/mol]")
for d, e in zip(distances, energies):
    print(f"{d:.2f}    {e:.3f}")

Note

To execute this PLAMS script:

• Download He2DissociationCurve.py

• $AMSBIN/plams He2DissociationCurve.py

Output

[10:45:48] PLAMS working folder: scratch/rundir.plams.He2DissociationCurve/plams_workdir
[10:45:48] JOB dist_2.20 STARTED
[10:45:48] JOB dist_2.20 RUNNING
[10:45:49] JOB dist_2.20 FINISHED
[10:45:49] JOB dist_2.20 SUCCESSFUL
...
[10:45:57] JOB dist_4.00 STARTED
[10:45:57] JOB dist_4.00 RUNNING
[10:45:58] JOB dist_4.00 FINISHED
[10:45:58] JOB dist_4.00 SUCCESSFUL
== Results ==
d[A]    E[kcal/mol]
2.20    0.230
2.40    -0.054
2.60    -0.127
2.80    -0.122
3.00    -0.094
3.20    -0.066
3.40    -0.045
3.60    -0.030
3.80    -0.020
4.00    -0.013
[10:45:58] PLAMS run finished. Goodbye
Test duration in seconds: 10