S66: A Well-balanced Database of Benchmark Interaction Energies Relevant to Biomolecular Structures

With numerous new quantum chemistry methods being developed in recent years and the promise of even more new methods to be developed in the near future, it is clearly critical that highly accurate, well-balanced, reference data for many different atomic and molecular properties be available for the parametrization and validation of these methods. One area of research that is of particular importance in many areas of chemistry, biology, and material science is the study of noncovalent interactions. Because these interactions are often strongly influenced by correlation effects, it is necessary to use computationally expensive high-order wave function methods to describe them accurately. Here, we present a large new database of interaction energies calculated using an accurate CCSD(T)/CBS scheme. Data are presented for 66 molecular complexes, at their reference equilibrium geometries and at 8 points systematically exploring their dissociation curves; in total, the database contains 594 points: 66 at equilibrium geometries, and 528 in dissociation curves. The data set is designed to cover the most common types of noncovalent interactions in biomolecules, while keeping a balanced representation of dispersion and electrostatic contributions. The data set is therefore well suited for testing and development of methods applicable to bioorganic systems. In addition to the benchmark CCSD(T) results, we also provide decompositions of the interaction energies by means of DFT-SAPT calculations. The data set was used to test several correlated QM methods, including those parametrized specifically for noncovalent interactions. Among these, the SCS-MI-CCSD method outperforms all other tested methods, with a root-mean-square error of 0.08 kcal/mol for the S66 data set

Theoretical study of the stacking behavior of selected polycondensed aromatic hydrocarbons with various symmetries

Stacked dimers of four polycondensed aromatic hydrocarbons, with structures varying from high to reduced symmetries, have been calculated with dispersion-corrected density functional theory. The configurations of the stacked dimers are readily classified by two in-plane displacements and a relative rotation. The potential energy surface in these three coordinates was calculated with rigid monomers and appears to be slightly flat. Full geometry optimization was performed for selected low-energy structures, resulting in an energy ranking of a series of conformations whose geometries were characterized in considerable detail. The dissociation energy values reveal a clear preference for the symmetrical disk-shaped and triangular structures to dimerize into two in-plane-displaced arrangements, whereas the less symmetrical trapezoidal structures show a tendency to stack in displaced antiparallel over parallel arrangements. According to methodical checks, the key computational results, namely, the shape of the potential energy surface and the geometrical structures and energy ranking of dimer conformations, are essentially insensitive to computational assumptions such as the atomic orbital basis set and density functional chosen. This is shown in particular for the basis set superposition error, which, for the selected level of theory [B97-D3(BJ)/TZV(d,p)] was estimated by the counterpoise correction procedure to be in the narrow range between 7% and 8% of the uncorrected dissociation energies