Density-Functional Errors in Alkanes: A Real-Space Perspective.


Journal Article

Density-functional theory (DFT) approximations are known to give systematic errors for isodesmic reaction energies of n-alkanes to form ethane. Several explanations have been proposed, involving both the exchange or correlation nature of the problem and its distance range (i.e., medium-range or long-range interactions). In this work, a new isodesmic reaction is defined to demonstrate that the reaction energy differences originate from localized interactions between contiguous CH2 units in the n-alkane, i.e., from 1,3 interactions. Furthermore, we introduce a real-space interpretation of the error based on changes in electron density, described by our recently developed Non-Covalent Interactions (NCI) method. The reduced density gradient has smaller values for noncovalent 1,3 interactions in n-alkane reactants compared to ethane products. The gradient contribution to the exchange energy is consequently reduced, giving a constant energy bias against each propane unit in an n-alkane. Differences in exchange energy for grid points within the NCI regions are shown to be responsible for the reaction-energy errors. This is also demonstrated to be the source of error in Diels-Alder addition barrier heights obtained with GGA-based hybrid functionals.

Full Text

Duke Authors

Cited Authors

  • Johnson, ER; Contreras-García, J; Yang, W

Published Date

  • August 2, 2012

Published In

Volume / Issue

  • 8 / 8

Start / End Page

  • 2676 - 2681

PubMed ID

  • 26592113

Pubmed Central ID

  • 26592113

Electronic International Standard Serial Number (EISSN)

  • 1549-9626

International Standard Serial Number (ISSN)

  • 1549-9618

Digital Object Identifier (DOI)

  • 10.1021/ct300412g


  • eng