Theoretical study of chemical reactions using density functional methods with nonlocal corrections

Abstract

Density functional calculations have been performed for the C-H bond dissociation of methane, N2 dissociation, the C-H bond dissociation of acetylene, ethylene, and vinyl radical, the rotational barrier of acrolein, and the relative energies for isomers and transition structures of diazene. It is found that the nonlocal spin density (NLSD) approach brings significant improvements over the local spin density (LSD) energetics. In most of these systems, the accuracy of density functional methods is comparable to the best available correlated wave function based ab initio results.

Accurate MRCI study of ground-state N2H2 potential energy surface

“…The potential energy scan for dissociation of a hydrogen atom from trans-, cis-, and iso-N 2 H 2 has been calculated at the MRCI + Q/aug-cc-pVQZ level of theory. These figures collect all the structures of minima and transition states of N 2 H 2 found in the present study, while Table 2 compares the transition states geometries, frequencies and relative energies with data from other theoretical works [1,2,13,12]. There has been a dispute in the literature on whether the trans-cis isomerization occurs via one or two transition states connecting these structures (inversional-TS1 or rotational-TS2) or rather that all rearrangements within the N 2 H 2 system evolve through the dissociation-recombination pathway involving TS6.…”

“…There have been several theoretical [1][2][3][4][5][6][7][8][9][10][11][12][13] and experimental [14][15][16][17][18][19] studies of the title system (a more complete list of earlier theoretical and experimental work is given in Refs. [3,2]).…”

“…Some of these studies focused on the determination of accurate geometries, frequencies and relative stabilities of three local minima: trans-, cis-, and iso-N 2 H 2 [3,7,[14][15][16][17][18][19]11,10]. Moreover, there has been considerable theoretical work [2,1,9,4,8,6,5,12,13] on the determination of the barriers involved in the diimide isomerization or formation processes, often for testing the accuracy of theoretical methods that are used to study chemical reactions [13,12,4,6]. All published work agrees on the structures of the above minima (trans-, cis-, and iso-) for N 2 H 2 , although the agreement for transition states (TSs) stands only for the TS associated to the trans-iso conversion.…”

“…For the other TSs, discrepancies exist between the various theoretical results. In particular, for the trans-cis conversion, some papers predict both rotational and inversional reaction paths [2,9,8] while others infer it to occur by inversion [6,12,13] or rotation [1] only.…”

Benchmark ab initio thermochemistry of the isomers of diimide, N2H2, using accurate computed structures and anharmonic force fields

“…[23][24][25]21,26]) and density functional (e.g. [27,28]) calculations on the relative stability of the trans-diazene, cis-diazene, and isodiazene isomers have consistently shown a stability ordering trans > cis > iso, as well as high (in excess of 40 kcal/mol) isomerization barriers between the isomers. (Very recently, the rigid cis-trans rotation of the molecule was proposed and studied [29] as a test case for a new multireference coupled cluster method [29], the transition state being a 'real-life' alternative for H 4 as an essentially perfect two-configuration reference problem.…”