Non-adiabatic coupling and conical intersection(s) between potential energy surfaces for HeH2+.

By computing the non-adiabatic coupling terms and the adiabatic-to-diabatic transformation angle along closed contours in nuclear configuration space using the CASSCF method and the aug-cc-pVTZ basis set for the lowest three electronic states of HeH2+, we explore the conical intersection between states in near collinear and noncollinear geometries, particularly in the C2v geometry. [ABSTRACT FROM AUTHOR]