n-Alkane isodesmic reaction energy errors in density functional theory are due to electron correlation effects

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Standard Density Functional Theory (DFT) calculations exhibit systematic errors for isodesmic reactions of n-alkanes.
• Accurate calculation of reaction energies is crucial for understanding chemical processes and developing new materials.

Purpose of the Study:

• To investigate the performance of advanced computational methods in accurately reproducing isodesmic reaction energies of n-alkanes.
• To identify the source of systematic errors in standard DFT calculations for these systems.

Main Methods:

• Utilized Second-order Møller–Plesset perturbation theory with spin-component scaling (SCS-MP2).
• Employed dispersion-corrected double-hybrid density functionals.
• Calculated highly accurate coupled cluster with singles, doubles, and perturbative triples (CCSD(T))//Complete Basis Set (CBS) data for benchmarking.

Main Results:

• SCS-MP2 and dispersion-corrected double-hybrid functionals successfully reproduced isodesmic reaction energies of n-alkanes.
• The failure of conventional DFT was attributed to inaccurate accounting of medium-range electron correlation, specifically attractive 1,3-interactions (proto-branching), rather than a lack of long-range exchange.

Conclusions:

• Advanced computational methods like SCS-MP2 and double-hybrid functionals offer significant improvements over standard DFT for alkane thermochemistry.
• Understanding the role of medium-range electron correlation is key to developing more accurate theoretical models for chemical reactions.