"Gold-Standard" $Δ$-Machine Learned and Transferable Potential for Linear Alkanes

Abstract: The conformational properties of linear alkanes, C$<em>n$H$</em>{2n+2}$, have been of intense interest for many years. Experiments and corresponding electronic structure calculations were first reported in the mid-2000s and continue to the present time. These focus on the minimum chain length where the transition from the linear minimum to the hairpin minimum occurs. We recently reported a transferable many-body permutationally invariant polynomial (MB-PIP) for linear alkanes using B3LYP electronic energies, which do not account for dispersion. Here we report a $\Delta$-ML approach to elevate this B3LYP-based and new PBE0+MBD MB-PIP potentials using PNO-LCCSD(T)-F12 energies. The new $\Delta$-corrected potentials predict the difference in these minima accurately, compared to benchmark CCSD(T) results, over the range C$<em>{12}$H$</em>{28}$ to C$<em>{28}$H$</em>{58}$. Vibrational power spectra are also reported for C$<em>{14}$H$</em>{30}$ and C$<em>{30}$H$</em>{62}$ using the uncorrected and $\Delta$-ML B3LYP. These new PIP-MB potentials for linear alkanes are the most accurate ones currently available and can be used in studies of properties of linear alkanes.