Comparison of Aromatic NH ...pi, OH...pi, and CH ...pi Interactions of Alanine using MP2, CCSD, and DFT methods

Abstract

A comparison of the performance of various density functional methods including long-ranee corrected and dispersion corrected methods [MPW1PW91, B3LYP, B3PW91, B97-D, B1B95, MPWB1K, M06-2X, SVWN5, omega B97XD, long-range correction (LC)-omega PBE, and CAM-B3LYP using 6-31+G(d,p) basis set] in the study of CH center dot center dot center dot pi, OH center dot center dot center dot pi, and NH center dot center dot center dot pi interactions were done using weak complexes of neutral (A) and cationic (A(+)) forms of alanine with benzene by taking the Moller-Plesset (MP2)/6-31+G(d,p) results as the reference. Further, the binding energies of the neutral alanine-benzene complexes were assessed at coupled cluster (CCSD)/6-31G (d,p) method. Analysis of the molecular geometries and interaction energies at density functional theory (DFT), MP2, CCSD methods and CCSD(T) single point level reveal that MP2 is the best overall performer for noncovalent interactions giving accuracy close to CCSD method. MPWB1K fared better in interaction energy calculations than other DFT methods. In the case of M06-2X. SVWN5, and the dispersion corrected B97-D, the interaction energies are significantly overrated for neutral systems compared to other methods. However, for cationic systems. B97-D yields structures and interaction energies similar to MP2 and MPWB1K methods. Among the long-range corrected methods. LC-omega PBE and CAM-B3LYP methods show close agreement with MP2 values while omega B97XD energies are notably higher than MP2 values.