Single-Point Energy

Python API · stjames models · API example

How it works

Calculate the energy of a fixed geometry without relaxing its atoms. This is useful for comparing conformers or evaluating a previously optimized structure with a different method. The result describes the supplied geometry; it does not find a lower-energy structure.

Settings

• Tasks: select "Energy" alone for a single-point energy calculation. Selecting "Optimize" or "Optimize (TS)" changes the geometry before reporting its final energy.
• Method and engine: choose "Method" and a compatible "Engine." Check that the method supports the elements, charge, and spin state of your structure.
• Basis set: choose "Basis set" when the method requires one. A larger basis can improve accuracy but increases calculation cost.
• Corrections: use "Corrections" to select a supported dispersion correction when appropriate for the method. Dispersion describes attractions that can affect conformer and intermolecular energies.
• Solvent: choose "Solvent" and its "Model" for an implicit-solvent calculation, or leave solvent unset for a gas-phase calculation. Available models depend on the method and engine.

Notes

For conformer rankings, compare energies using the same method, basis set, corrections, solvent model, charge, and spin state. Absolute energies of molecules with different compositions do not directly indicate which is more stable.

An energy-only calculation does not provide vibrational zero-point, thermal, or entropy corrections, or confirm that the structure is a minimum. Those require frequency analysis. Electronic energy differences alone therefore do not give Gibbs free-energy differences.

For API calculations using COSMO-RS, the reported energy is the gas-phase electronic energy plus the solvation free energy at 298.15 K. COSMO-RS basic calculations support molecular structures and the energy task only.