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Chemistry International
Vol. 24, No. 2
March 2002


Highlights from Pure and Applied Chemistry

Quantum Chemical B3LYP/cc-pvqz
Computation of Ground-State Structures and Properties of Small Molecules with Atoms of Z 18 (Hydrogen to Argon) (IUPAC Technical Report)

by Rudolf Janoschek
Pure and Applied Chemistry Vol. 73, No. 9, pp. 1521-1553 (2001)

Since density functional theory achieved a remarkable breakthrough in computational chemistry, the important general question "How reliable are quantum chemical calculations for spectroscopic properties?" should be answered anew. In this project, the most successful density functionals, namely the Becke B3LYP functionals, and the correlationconsistent polarized valence quadruple zeta basis sets (cc-pvqz) are applied to small molecules. In particular, the complete set of experimentally known diatomic molecules formed by the atoms H to Ar (there are 214 systems) is uniformly calculated, and calculated spectroscopic properties are compared with experimental ones.

Computationally demanding molecules, such as open-shell systems, anions, or noble gas compounds, are included in this study. Investigated spectroscopic properties include spectroscopic ground state, equilibrium internuclear distance, harmonic vibrational wavenumber, anharmonicity, vibrational absolute absorption intensity, electric dipole moment, ionization energy, and dissociation energy. The same computational method has also been applied to the ground-state geometries of 56 polyatomic molecules up to the size of benzene. Special sections are dedicated to nuclear magnetic resonance chemical shifts and isotropic hyperfine coupling constants. Each set of systems for a chosen property is statistically analyzed, and the above important question �How reliable . . . ?� is mathematically answered by the mean absolute deviation between calculated and experimental data, as well as by the worst agreement. In addi-tion to presentation of numerous quantum chemically calculated spectroscopic properties, a corresponding updated list of references for experimentally determined properties is presented.





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