Design of low band gap polymers employing density functional theory?hybrid functionals ameliorate band gap problem

✍ Scribed by Salzner, U.; Lagowski, J. B.; Pickup, P. G.; Poirier, R. A.

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 224 KB
• Volume: 18
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/(sici)1096-987x(19971130)18:15<1943::aid-jcc9>3.0.co;2-o

✦ Synopsis

Band gaps in solids and excitation energies in finite systems are underestimated significantly if estimated from differences between eigenvalues Ž . obtained within the local spin density approximation LSDA . In this article we present results on 20 small-and medium-sized -systems which show that HOMO᎐LUMO energy differences obtained with the B3LYP, B3P86, and B3PW91 functionals are in good agreement with vertical excitation energies from UVabsorption spectra. The improvement is a result of the use of the exact Hartree᎐Fock exchange with hybrid methods. Negative HOMO energies and negative LUMO energies do not provide good estimates for IPs and EAs. In contrast to Hartree᎐Fock theory, where IPs are approximated well and EAs are given poorly, DFT hybrid methods underestimate IPs and EAs by about the same amount. LSDA yields reasonable EAs but poor IPs.