Direct Force Constants for Spectroscopic Analysis from Quantum Mechanical Information: SmartField Force Field

The classical modelling of organic molecules is based on force fields of commercial standard libraries, which might be limited and can be potentially inaccurate for compounds outside the data set. One common solution to this is the derivation of ad-hoc force field parameters for new molecules. However, this approach might be long and expensive even for experienced chemist. In this prospective, we propose an integrated and automated toolkit, called SmartField, to obtain intra- and intermolecular force field parameters with a good degree of accuracy and a margin of transferability. SmartField extracts all bonded parameters directly from the quantum mechanical Hessian, while CM5 charge, and Lennard-Jones parameter are retrived from standard outputs. We assessed the accuracy of SmartField by comparing vibrational frequencies and geometries of data set of rigid and flexible compounds with their quantum counterpart. Furthermore, SmartField parameters are employed for the computation of the absorption and emission spectra of the indole moiety, and tryptophan amino acid, in water. A direct comparison with the available experimental data is good and it gives a support of SmartField-derived force fields, which can be exploited for the modelling of novel and more complex compounds.