Comparison of aromatic NH···π, OH···π, and CH···π interactions of alanine using MP2, CCSD, and DFT methods

A comparison of the performance of various density functional methods including long-range corrected and dispersion corrected methods [MPW1PW91, B3LYP, B3PW91, B97-D, B1B95, MPWB1K, M06-2X, SVWN5, ωB97XD, long-range correction (LC)-ωPBE, and CAM-B3LYP using 6-31+G(d,p) basis set] in the study of CH···π, OH···π, and NH···π interactions were done using weak complexes of neutral (A) and cationic (A(+)) forms of alanine with benzene by taking the Møller-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-ωPBE and CAM-B3LYP methods show close agreement with MP2 values while ωB97XD energies are notably higher than MP2 values.