Configuration interaction singles based on the real-space numerical grid method: Kohn–Sham versus Hartree–Fock orbitals. Issue 47 (14th April 2015)

• Record Type: Journal Article
• Authors: Kim, Jaewook; Hong, Kwangwoo; Choi, Sunghwan; Hwang, Sang-Yeon; Youn Kim, Woo
• Is Part Of: Physical chemistry chemical physics. Volume 17:Issue 47(2015)
• Page Start: 31434
• Page End: 31443
• Publication Date: 2015-04-14
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c5cp00352k
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : We developed a program code of CIS based on a numerical grid method and showed that Kohn–Sham orbitals from the Krieger–Li–Iafrate (KLI) approximation provide better reference configurations for CIS than the standard Hartree–Fock and Kohn–Sham orbitals. Abstract : We developed a program code of configuration interaction singles (CIS) based on a numerical grid method. We used Kohn–Sham (KS) as well as Hartree–Fock (HF) orbitals as a reference configuration and Lagrange-sinc functions as a basis set. Our calculations show that KS-CIS is more cost-effective and more accurate than HF-CIS. The former is due to the fact that the non-local HF exchange potential greatly reduces the sparsity of the Hamiltonian matrix in grid-based methods. The latter is because the energy gaps between KS occupied and virtual orbitals are already closer to vertical excitation energies and thus KS-CIS needs small corrections, whereas HF results in much larger energy gaps and more diffuse virtual orbitals. KS-CIS using the Lagrange-sinc basis set also shows a better or a similar accuracy to smaller orbital space compared to the standard HF-CIS using Gaussian basis sets. In particular, KS orbitals from an exact exchange potential by the Krieger–Li–Iafrate approximation lead to more accurate excitation energies than those from conventional (semi-) local exchange–correlation potentials.