Intermolecular Interactions of Linear Alkane (N ≤ 18) Dimers: A High Accuracy Theoretical Study.

This work systematically investigates the intermolecular interactions in n-alkane (C n H2n+2, n = 1-18) dimers through high-accuracy DLPNO-CCSD-(T1)/CBS-(aug2/3)//M05-2X-D3/6-31G** calculations. The relative errors of interaction energies are below 5% with respect to CCSD-(T)/CBS-(aug-cc-2/3)//M05-2X-D3/6-31G** benchmarks. The BSSE-corrected results are reported from -2.2 kJ/mol (n = 1) to -62.6 kJ/mol (n = 18). The interaction energy (ΔE) increases linearly with chain length (n), as quantified by the equation ΔE(n) = -3.6n + 2.2 kJ/mol, providing a more accurate quantitative description compared to the previous MP2/CBS research. Moreover, thermodynamic analysis reveals that spontaneous dimerization starts from n ≥ 8 at 100 K. These findings provide a high-accuracy benchmark for noncovalent interactions in n-alkane dimers, deepening the understanding of van der Waals interaction strength, and providing valuable insights for molecular design.