Journal ArticleDOI
High-accuracy extrapolated ab initio thermochemistry. III. Additional improvements and overview
Michael E. Harding,Juana Vázquez,Branko Ruscic,Angela K. Wilson,Jürgen Gauss,John F. Stanton +5 more
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TLDR
Fortuitous cancellation of high-level effects is shown to give the overall HEAT strategy an accuracy that is, in fact, higher than most of its individual components.Abstract:
Effects of increased basis-set size as well as a correlated treatment of the diagonal Born-Oppenheimer approximation are studied within the context of the high-accuracy extrapolated ab initio thermochemistry (HEAT) theoretical model chemistry. It is found that the addition of these ostensible improvements does little to increase the overall accuracy of HEAT for the determination of molecular atomization energies. Fortuitous cancellation of high-level effects is shown to give the overall HEAT strategy an accuracy that is, in fact, higher than most of its individual components. In addition, the issue of core-valence electron correlation separation is explored; it is found that approximate additive treatments of the two effects have limitations that are significant in the realm of <1kJmol−1 theoretical thermochemistry.read more
Citations
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A hierarchy of homodesmotic reactions for thermochemistry.
TL;DR: It is demonstrated that RC4 and RC5 reactions provide bond separation enthalpies with errors consistently less than 0.4 kcal mol(-1) across a wide range of theoretical levels, performing significantly better than the other reaction types and far superior to atomization routes.
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Frequency and zero-point vibrational energy scale factors for double-hybrid density functionals (and other selected methods): can anharmonic force fields be avoided?
TL;DR: Uniform frequency scaling factors for true anharmonic fundamentals and ZPVEs obtained from quartic force fields are obtained and simple uniform scaling is clearly inadequate.
Journal ArticleDOI
Chemical accuracy in ab initio thermochemistry and spectroscopy: current strategies and future challenges
TL;DR: The current state of the art in wave function-based electronic structure methods is illustrated via discussions of the most important effects incorporated into a selection of high-accuracy methods chosen from the chemical literature as discussed by the authors.
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W4-11: A high-confidence benchmark dataset for computational thermochemistry derived from first-principles W4 data
TL;DR: The W4-11 dataset as discussed by the authors provides a broad spectrum of bonding situations and multireference character, and as such is an excellent, quasi-automated benchmark for parametrization and validation of more approximate methods (such as DFT functionals and composite methods).
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Fully anharmonic IR and Raman spectra of medium-size molecular systems: accuracy and interpretation
TL;DR: This perspective sketches the recent developments in the research group toward the development of a robust and user-friendly virtual spectrometer rooted in second-order vibrational perturbation theory (VPT2) and usable also by non-specialists essentially as a black-box procedure.
References
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Gaussian basis sets for use in correlated molecular calculations. I. The atoms boron through neon and hydrogen
TL;DR: In this paper, a detailed study of correlation effects in the oxygen atom was conducted, and it was shown that primitive basis sets of primitive Gaussian functions effectively and efficiently describe correlation effects.
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Electron affinities of the first-row atoms revisited. Systematic basis sets and wave functions
TL;DR: In this paper, a reliable procedure for calculating the electron affinity of an atom and present results for hydrogen, boron, carbon, oxygen, and fluorine (hydrogen is included for completeness).
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A fifth-order perturbation comparison of electron correlation theories
TL;DR: In this paper, a new augmented version of coupled-cluster theory, denoted as CCSD(T), is proposed to remedy some of the deficiencies of previous augmented coupledcluster models.