Abstract
AbstractTwo‐level factorial design (FD) and principal component (PC) models are used to determine the effects of wave function modifications on calculated HC and CC harmonic stretching frequencies for the HCCH, HCCF, HCCCl, HCCCCH, HCCCN and HCCCH3 molecules. Our results have shown that valence (val), diffuse (dif), polarization (pol), and electron correlation (corr) main effects as well as some second‐order interaction effects are significant to build factorial models for these vibrational frequencies. For instance, when valence and diffuse functions are introduced in the basis set, the calculated HC and CC stretching frequencies decrease. However, this reduction is much more accentuated when the electron correlation effect is introduced in the Hartree‐Fock wave functions. By far, the corr main effect is the most important one on the HC and CC frequency values. The MP2 electron correlation effect provokes an increment of −157.4 cm−1 and −283.8 cm−1 on the HC and CC stretching frequencies, respectively, whereas the dif effect produces only a reduction of −9.1 cm−1 and −12.9 cm−1 on these frequencies, respectively. The inclusion of Møller–Plesset 2 perturbation in the Hartree‐Fock wave functions also produces an important pol–corr interaction effect on the HC and CC stretching frequencies, increasing their values by +45.2 cm−1 and +17.3 cm−1, respectively. Algebraic models were then established to explain how calculated HC and CC stretching frequencies depend on characteristics of the molecular orbital wave functions. These models were successful in reproducing calculated HC and CC frequency values for the HCN and CH3CCCH3 molcules, which were not included in the training set. The principal component analysis has revealed that the calculated HC and CC stretching frequencies can be adequately described by a single principal component. It is capable of explaining more than 99% of the total data variance. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008
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