Geometry Optimization of Large and Flexible van der Waals Dimers: A Fragmentation-Reconstruction Approach

A novel approach for exploring the energy minima of the potential energy surface of large and flexible van der Waals dimers is proposed and tested. The total dimer energy is divided into intra- and intermolecular contributions, which can be computed at different levels of theory. The intermolecular energy, which is the time-consuming part of the calculation, is computed by means of the fragmentation reconstruction method (FRM), making possible the calculation of the interaction energy of large molecules. The method is validated by performing geometry optimizations through a quasi-Newton technique on two benchmark medium-sized systems, where the comparison with a direct ab initio calculation is still computationally feasible. In both cases, good agreement is achieved between geometries and energies of the resulting energy minima.