ASE Manual Release 3.6.1.2825 CAMd - CampOS Wiki

ASE Manual, Release 3.6.1.2828
Example
symmetrynumber [integer] symmetry number of the molecule. See, for example, Table 10.1 and Appendix
B of C. Cramer “Essentials of Computational Chemistry”, 2nd Ed.
spin [float] the total electronic spin. (0 for molecules in which all electrons are paired, 0.5 for a free radical
with a single unpaired electron, 1.0 for a triplet with two unpaired electrons, such as O_2.)
get_enthalpy(temperature, verbose=True)
Returns the enthalpy, in eV, in the ideal gas approximation at a specified temperature (K).
get_entropy(temperature, pressure, verbose=True)
Returns the entropy, in eV/K, in the ideal gas approximation at a specified temperature (K) and pressure
(Pa).
get_free_energy(temperature, pressure, verbose=True)
Returns the free energy, in eV, in the ideal gas approximation at a specified temperature (K) and
pressure (Pa).
The IdealGasThermo class would generally be called after an energy optimization and a vibrational analysis.
The user needs to supply certain parameters if the entropy or free energy are desired, such as the geometry and
symmetry number. An example on the nitrogen molecule is:
from ase.data.molecules import molecule
from ase.calculators.emt import EMT
from ase.optimize import QuasiNewton
from ase.vibrations import Vibrations
from ase.thermochemistry import IdealGasThermo
atoms = molecule(’N2’)
atoms.set_calculator(EMT())
dyn = QuasiNewton(atoms)
dyn.run(fmax=0.01)
electronicenergy = atoms.get_potential_energy()
vib = Vibrations(atoms)
vib.run()
vib_energies = vib.get_energies()
thermo = IdealGasThermo(vib_energies=vib_energies,
electronicenergy=electronicenergy, atoms=atoms,
geometry=’linear’, symmetrynumber=2, spin=0)
G = thermo.get_free_energy(temperature=298.15, pressure=101325.)
This will give the thermodynamic summary output:
Enthalpy components at T = 298.15 K:
===============================
E_elec 0.000 eV
E_ZPE 0.116 eV
Cv_trans (0->T) 0.039 eV
Cv_rot (0->T) 0.026 eV
Cv_vib (0->T) 0.000 eV
(C_v -> C_p) 0.026 eV
-------------------------------
H 0.206 eV
===============================
Entropy components at T = 298.15 K and P = 101325.0 Pa:
=================================================
S T*S
S_trans (1 atm) 0.0015579 eV/K 0.464 eV
S_rot 0.0004314 eV/K 0.129 eV
174 Chapter 7. Documentation for modules in ASE