title: Deconstructing the ONIOM Hessian: Investigating Method Combinations for Transition Structures.
abstract: Developments in biochemistry and materials sciences have led to increasing interest in the reactivity of large chemical systems, presenting theoretical and computational challenges that can be addressed with hybrid methods such as ONIOM. Here, we show that the diagonalized ONIOM Hessian can be partitioned/deconstructed into contributions from the individual subcalculations-indicating the curvature of their potential energy surfaces (PESs)-without increasing the computational cost. The resulting pseudofrequencies have particular application in the study of transition structures and higher-order saddle points with ONIOM, where we find that an imaginary frequency may result from combining subcalculations for which the corresponding vibrational frequencies are all real. Two cycloaddition reactions, including functionalization of a 150 atom (5,5) single-walled carbon nanotube, demonstrate how this analysis of pseudofrequencies allows identification of critical points where further exploratory work should be carried out to ensure that the ONIOM PES correctly approximates the target.
authors.affiliation: Gaussian, Inc. , 340 Quinnipiac St Bldg 40, Wallingford, Connecticut 06492, United States.|Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School , Worcester, Massachusetts 01605, United States.
authors.forename: Thom
authors.initials: T
authors.lastname: Vreven
authors.affiliation: Department of Chemistry, Imperial College , London, SW7 2AZ, United Kingdom.
authors.forename: Lee M
authors.initials: LM
authors.lastname: Thompson
authors.affiliation: Department of Chemistry, Imperial College , London, SW7 2AZ, United Kingdom.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Larkin
authors.affiliation: Department of Chemistry, University College , London, WC1H 0AJ, United Kingdom.
authors.forename: Ian
authors.initials: I
authors.lastname: Kirker
authors.affiliation: Department of Chemistry, Imperial College , London, SW7 2AZ, United Kingdom.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Bearpark