VPT2 Calculations of Vibrational Energies of CH ₃ COOC ₆ H ₄ COOH Done in Seconds on a Laptop Using a Machine Learned Potential

O and protonated oxalate as the test cases. The Fortran software is applied to 21-atom aspirin using a fast MLP reported by us. Despite the fact that there are 32,509 unique cubic force constants for aspirin, the computer time to calculate them using this MLP is trivial, i.e., around 1 min. The new software provides an efficient way to calculate quantum anharmonic energies, using the established VPT2 methodology, for machine learned potentials of large molecules.