Thermochemical Trends in Carbon Chain Molecules HC2kH/HC2k-1H (k = 1−6) Studied by Explicitly Correlated CCSD(T)-F12b Composite Methods

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Original languageEnglish
Pages (from-to)5385–5396
Journal / PublicationJournal of Physical Chemistry A
Issue number24
Online published14 Jun 2021
Publication statusPublished - 24 Jun 2021


We present a composite procedure based on explicitly correlated CCSD(T)-F12 calculations for accurate energetic predictions for carbon chain molecules HCnH encompassing both the even (HC2kH) and odd series (HC2k-1H), with the shorter members playing a key role in the evolution of cosmic carbon compounds in both circumstellar envelopes and interstellar medium. This approach considers the contributions of core-valence correlation, scalar relativistic effect, spin-orbit coupling, and zero-point vibrational energy in an additive manner. The computed ionization energies demonstrate outstanding agreement (±0.07 eV) up to a chain size of k = 6 and the literature heats of formation for k ≤ 2 are reproduced with "chemical accuracy"of 1 kcal mol-1. Among the various corrections included, the importance of core-valence correlation effect has been highlighted in the thermochemical calculations for carbon chain growth. The thermochemical trend toward infinite length is also highlighted by extrapolation of ionization energy and triplet-singlet splitting at the CCSD(T) level for k up to 15. The correlation between the end-group effect and the even-odd parity effect observed for HCnH chains has been established with the aid of intrinsic bond orbital localization.

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