Related Experiment Video
Updated: Oct 27, 2025

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
Size-consistent explicitly correlated triple excitation correction
Mihály Kállay1, Réka A Horváth1, László Gyevi-Nagy1
1Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, P.O. Box 91, Budapest H-1521, Hungary.
Abstract:
A new approach is proposed to reduce the basis set incompleteness error of the triple excitation correction in explicitly correlated coupled-cluster singles and doubles with perturbative triples calculations. Our method is similar to the intuitive triples correction approach of Knizia et al. [J. Chem. Phys. 130, 054104 (2009)] but, in contrast to the latter, is size-consistent. The new approximation is easy to implement, and its overhead is negligible with respect to the conventional (T) correction. The performance of the approach is assessed for atomization, reaction, and interaction energies as well as for bond lengths and harmonic vibrational frequencies. The advantages of its size consistency are also demonstrated.
Related Concept Videos
¹H NMR: Interpreting Distorted and Overlapping Signals
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule
NMR Spectrometers: Resolution and Error Correction
Spin–Spin Coupling Constant: Overview
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
π Electron Effects on Chemical Shift: Overview
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...

