## Abstract

The performance of a large variety of contemporary density functional theory (DFT), double-hybrid DFT, and high-level Gaussian-n (Gn) procedures has been evaluated for the calculation of bond dissociation energies (BDEs) and radical stabilization energies (RSEs) associated with N-X bonds (X = H, Cl). The chosen set of 62 N-X systems (31 N-H and 31 N-Cl) span a wide range of biologically relevant species. As reference values, we used benchmark-quality W2w data that we recently obtained as part of a systematic thermochemical study of substituent effects in these systems. Of the Gn schemes, the modified G4 procedures (G4-5H and G4(MP2)-6X) perform somewhat better than the corresponding standard G4 procedures for the N-X BDEs of these systems. For the N-H RSEs, G3X, G3X(MP2), G3X(MP2)-RAD, G4-5H, and G4(MP2)-6X emerge as excellent performers, with mean absolute deviations (MADs) from the benchmark W2w values of 0.9-1.4 kJ mol ^{-1}. However, for the N-Cl RSEs, G4 is the best performer, with an MAD of 1.7 kJ mol ^{-1}. The BDEs of both N-H and N-Cl bonds represent a challenge for DFT procedures. In particular, only a handful of functionals (namely, B3P86, M05-2X, M06-2X, and ROB2-PLYP) perform well, with MADs â 4.5 kJ mol ^{-1} for both bond types. Nearly all of the considered DFT procedures perform significantly better for the computation of RSEs, due to a significantly larger degree of error cancelation compared with the BDEs. For the RSEs, BH&HLYP, M05-2X, M06, M06-2X, BMK, PBE0, B2-PLYP, B2GP-PLYP, B2T-PLYP, and ROB2-PLYP are the best performers, with MADs ≤ 4.2 kJ mol ^{-1}. Reliable values of N-H and N-Cl BDEs may be obtained by using the RSEs calculated by these functionals in conjunction with a thermochemical cycle involving an experimental (or high-level theoretical) BDE for the H _{2}N-H or H _{2}N-Cl bond.

Original language | English |
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Pages (from-to) | 1862-1878 |

Number of pages | 17 |

Journal | International Journal of Quantum Chemistry |

Volume | 112 |

Issue number | 8 |

DOIs | |

Publication status | Published - Apr 15 2012 |

## Keywords

- Gaussian-n theory
- bond dissociation energy
- density functional theory
- nitrogen-centered radicals
- radical stabilization energy

## ASJC Scopus subject areas

- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics
- Physical and Theoretical Chemistry