Structure and stability of [C2H4N]+ singlet‐state cations: Comparison between DFT and high‐level ab initio calculations

Abstract

AbstractThe stationary points of the [C2H4N]+ singlet potential energy surface have been characterized by means of B3LYP/6‐311+G(3df,2p) and G2(MP2) approaches. A comparison between both sets of results shows that, although both methods yield similar values for the relative stability of the local minima, they differ significantly regarding the stability of some transition states, in particular those corresponding to 1,3‐H shift processes. This implies that the dynamics of the corresponding reaction may exhibit substantial differences if based on B3LYP or high‐level ab initio potential surfaces. The attachment of N+ to the CC bond of ethylene is preceded by a charge transfer and, as a consequence, a symmetry breaking problem arises. Our results show that inclusion of high‐order correlation contributions through the participation of triple excitations may be crucial. The B3LYP method is not a good alternative to treat this problem due to the spin contamination of the unrestricted treatment. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003