Transition states, reaction paths, and thermochemistry using the nuclear–electronic orbital analytic Hessian

The nuclear–electronic orbital (NEO) method is a multicomponent quantum chemistry theory that describes electronic and nuclear effects simultaneously while avoiding the Born–Oppenheimer approximation for certain nuclei. Typically specified hydrogen nuclei are treated mechanically at same level as electrons, NEO potential energy surface depends on classical coordinates. This approach includes such zero-point delocalization directly into surface. An extended depending expectation values of incorporates coupling between Herein, theoretical methodology developed to optimize characterize stationary points standard or surface, generate minimum path from transition state down corresponding reactant product, compute thermochemical properties. For this purpose, analytic coordinate Hessian implemented Hartree–Fock theory. These Hessians used study SN2 reaction ClCH3Cl? hydride transfer C4H9+. each system, analysis single imaginary mode intrinsic along identifies dominant motions driving chemical reaction. Visualization protonic orbitals illustrates coupled beyond approximation. work provides foundation applying various correlated levels wide range reactions.