Calculation of Gas-phase Standard Formation Enthalpy via Ring-Preserved Connectivity-Based Hierarchy and Automatic Bond Separation Reaction Platform

Abstract

Bond separation reaction (BSR) is an effective scheme to derive reliable thermochemical properties by systematic error cancellation, while some challenges exist before its wide applications. The traditional BSR schemes are less feasible to cyclic molecules, and automatic BSR programs are not yet fully developed, unbeneficial to maintain the reliability and efficiency of BSR. Herein, we propose an improved scheme of BSR, the Ring-Preserved Connectivity-Based Hierarchy (RCBH) scheme, to enhance the predicted accuracy of gas-phase standard enthalpy of formation (EOF) by quantum chemical calculations. The accuracy and time–cost of RCBH scheme are tested at various DFT levels, involving 12 functionals and 6 basis sets, with samples covering 250 cyclic organic molecules. The superiority of RCBH in calculating EOF is verified, with M062X/6-31 + G(2df,p) recommended as the most cost-effective DFT level, which can approach the accuracy of G4 with only 4% CPU-time of G4. The EOFs calculated by M062X/6-31 + G(2df,p) with RCBH correction are highly consistent with the experimental measurements, with a MAE of 1.1 kcal/mol. We also develop an automated BSR software package, Automatic Bond Separation Reaction Platform (ABSRP), feasible for all categories of organic molecules. The RCBH scheme and ABSRP are expected to be used in calculating other thermochemical properties of extensive categories of neutral organic molecules, with high accuracy while low computational cost.