UC Riverside

Noncovalent interactions are ubiquitous in chemistry. As a source of stabilization, they play an important role in many interesting chemical processes, such as protein folding, molecular recognition, molecular self-assembly, physical adsorption, etc. Accurate energy predictions from first principles on many-body systems like molecular crystals requires electronic structure methods able to describe various types of noncovalent interactions like hydrogen bonding, electrostatic, induction, and van der Waals dispersion across different intramolecular conformations and intermolecular arrangements with high and uniform accuracy. Besides accuracy, computational efficiency should be considered for practical applications. Here, fast and accurate electronic methods are developed to treat both two-body and three-body noncovalent interactions.

For two-body interactions, the MP2C method developed by Pitonak and Hesselmann proves to be a reliable method with affordable computational cost. To improve the computational efficiency of MP2C dispersion correction, we propose the use of monomer-centered basis sets instead of dimer-centered ones. For an individual dimer, this change accelerates the dispersion correction several-fold. For molecular crystals, 100-fold speedups for dispersion correction calculation are achieved by utilizing translational symmetry. To improve the computational efficiency of the MP2 part in MP2C method, we demonstrate that one can avoid calculating the unnecessary long-range MP2 correlations by attenuating the Coulomb operator, allowing the dispersion correction to handle the long-range interactions inexpensively. Utilizing excellent fortuitous cancellations between finite basis set errors, attenuation errors and correlation errors, further computational savings could be achieved by the use of small basis set to approach complete basis set limit quality results.

For three-body interactions, which are challenging for many widely-used, low-cost electronic structure methods, we propose a straightforward model that corrects conventional MP2 with a damped three-body Axilrod-Teller-Muto dispersion correction. The damping function compensates for the absence of higher-order dispersion contributions and non-additive short-range exchange terms not found in MP2. Examinations on trimer benchmark set and benzene crystal demonstrate the reliability of this model for various applications.