Multi-Fidelity Nx1D Hindered Rotor

Compute hindered-rotor-corrected thermochemistry with multi-fidelity surrogate modelling. A low-fidelity method handles optimisation, vibrations, and relaxed dihedral scans, then MufiTorsion strategically samples num_single_point_energies high-fidelity single-point energies per rotor to build a multi-fidelity Gaussian process model. The Tamkin Nx1D partition function is evaluated on the corrected potential energy surface.

Minimal Example

from atomiverse import (
    LevelOfTheory,
    MFNx1DHinderedRotor,
    gf2_xtb,
    wb97m_v_def2_tzvppd,
)

job = MFNx1DHinderedRotor(
    atoms=molecule,
    charge=0,
    multiplicity=1,
    level_of_theory=gf2_xtb,
    single_point_level_of_theory=wb97m_v_def2_tzvppd,
    dihedral_indices=[[0, 1, 2, 3]],
    num_single_point_energies=5,
    temperature_start=200.0,
    temperature_stop=800.0,
    temperature_step=50.0,
).submit()
result = job.result()

Inputs

Field	Type	Required	Description
atoms	Atoms	Yes	Input geometry (optimised automatically).
charge	int	No	Net charge. Default 0.
multiplicity	int	No	Spin multiplicity. Default 1, minimum 1.
level_of_theory	LevelOfTheory	Yes	Lo-fi method for optimisation, vibrations, scans.
single_point_level_of_theory	LevelOfTheory	Yes	Hi-fi method for single-point sampling.
dihedral_indices	list[list[int]]	Yes	One dihedral per rotor. Each inner list holds 4 zero-based atom indices.
num_single_point_energies	int	No	Hi-fi samples per rotor (after initial minimum). Default 3.
scan_step_size	float	No	Step size in degrees for lo-fi scans. Default 15.0.
temperature_start	float	No	First temperature in K. Default 200.0.
temperature_stop	float	No	Last temperature in K. Default 800.0.
temperature_step	float	No	Temperature increment in K. Default 50.0.

Results

Field	Type	Description
zpe_kj_per_mol	float	Zero-point energy in kJ/mol.
external_symmetry_number	int	External rotational symmetry number.
rotor_symmetry_numbers	list[int]	Rotor symmetry numbers (one per rotor).
rho_values	list[float]	Multi-fidelity scaling factor ρ per rotor.
properties	list[MFNx1DHinderedRotorTemperatureProperties]	Per-temperature thermodynamic properties.

Each entry in properties contains:

Field	Type	Description
temperature	float	Temperature in K.
internal_energy_kj_per_mol	float	Internal energy U in kJ/mol.
entropy_j_per_mol_k	float	Entropy S in J/(mol·K).
gibbs_energy_kj_per_mol	float	Gibbs free energy G in kJ/mol.
heat_capacity_j_per_mol_k	float	Heat capacity Cp in J/(mol·K).

Compute Resources

This job runs an optimisation, vibrations, N lo-fi scans, up to N × (1 + num_single_point_energies) high-fidelity single-point energies, and a Tamkin partition-function evaluation. The walltime multiplier is 360× the base tier walltime. Large molecules or many rotors are assigned higher resource tiers.