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A fully ab initio quartic force field of spectroscopic quality for SO_3 | | Jan M.L. Martin
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12 Aug 1998 | | Journal: | Spectrochimica Acta A 55, 713-722 (1999) | | Subject: | Chemical Physics | physics.chem-ph | | Abstract: | The quartic force field of SO$_3$ was computed fully ab initio using coupled cluster (CCSD(T)) methods and basis sets of up to $spdfgh$ quality. The effect of inner-shell correlation was taken into account. The addition of tight $d$ functions is found to be essential for accurate geometries and harmonic frequencies. The equilibrium geometry and vibrational fundamentals are reproduced to within 0.0003 AA and (on average) 1.15 cm^{-1}, respectively. We recommend the following revised values for the harmonic frequencies: $omega_1 = 1082.7, omega_2 = 502.6, omega_3 = 1415.4, omega_4 = 534.0 cm^{-1}$. In addition, we have shown that the addition of inner polarization functions to second-row elements is highly desirable even with more approximate methods like B3LYP, and greatly improves the quality of computed geometries and harmonic frequencies of second-row compounds at negligible extra computational cost. For larger such molecules, the B3LYP/VTZ+1 level of theory should be a very good compromise between accuracy and computational cost. | | Source: | arXiv, physics/9808012 | | Services: | Forum | Review | PDF | Favorites | |
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