Density functional study of the structures of small cycloalkanes

Abstract

Density-functional calculations with ultrasoft pseudopotentials and gradient-corrected nonlocal exchange-correlation functionals are performed to study the geometric structures and the binding energies of cyclopropane (C 3H 6), cyclobutane (C 4H 8), cyclopentane (C 5H 10), and cyclohexane (C 6H 12). Puckered ring structures are found to be energetically preferred to accommodate angle strain and torsion strain. The binding energy per carbon atom monotonically increases from 16.202 eV for ground-state cyclopropane to 16.576 eV for ground-state cyclohexane. In cyclohexane, where both the angle strain and torsion strain are reduced, the planar and the puckered conformations are found to have significantly different structures and binding energies whereas cyclobutane and cyclopentane show minor differences between the planar and the puckered conformations.