Evaluation of Uncertainty of Ideal-Gas Entropy and Heat Capacity Calculations by Density Functional Theory (DFT) for Molecules Containing Symmetrical Internal Rotors

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• 作者：Ctirad 膶ervinka ; Michal Fulem ; Kv臎toslav R暖啪i膷ka
• 刊名：Journal of Chemical & Engineering Data
• 出版年：2013
• 出版时间：May 9, 2013
• 年：2013
• 卷：58
• 期：5
• 页码：1382-1390
• 全文大小：509K
• 年卷期：v.58,no.5(May 9, 2013)
• ISSN：1520-5134

文摘

The uncertainty of thermophysical data is indispensable information when reporting both experimental and calculated values. In this paper, we present an evaluation of the uncertainty of the ideal-gas entropy and heat capacity calculations by density functional theory (DFT) for molecules containing symmetrical internal rotors. The rigid-rotor harmonic oscillator (RRHO) and one-dimensional hindered rotor (1-DHR) models are compared as well as the effect of the scale factors employed. The calculations of the standard ideal-gas entropy (S^g0) are performed for a selected set of 33 molecules for which reliable reference data were found in the literature. The RRHO model provides S^g0 with the absolute average percentage deviations (蟽_r) about 2 % from the reference data. Scaling the frequencies does not lead to any improvement when using the RRHO model. A significant improvement is achieved when the 1-DHR model and scale factors for low and high frequencies are applied simultaneously (蟽_r less than 0.3 %). The ideal-gas heat capacity (C_p^g0) calculations were tested on a set of 72 molecules. The RRHO model yields C_p^g0 values with 蟽_r up to 3 % at 300 K and 1 % at 1000 K while using the 1-DHR model coupled with a pair of scale factors lowers 蟽_r to less than 1.5 % and 0.5 % at 300 K and 1000 K, respectively.