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# Evaluation of uncertainty of ideal-gas entropy and heat capacity calculations by density functional theory (DFT) for molecules containing symmetrical internal rotors

- 1.0437069 - FZÚ 2015 RIV US eng J - Journal Article
**Červinka, C. - Fulem, Michal - Růžička, K.**

Evaluation of uncertainty of ideal-gas entropy and heat capacity calculations by density functional theory (DFT) for molecules containing symmetrical internal rotors.*Journal of Chemical and Engineering Data*. Roč. 58, č. 5 (2013), s. 1382-1390. ISSN 0021-9568. E-ISSN 1520-5134**Institutional support**: RVO:68378271**Keywords**: chemical thermodynamic properties * ab-initio calculation * vapor-pressure * xylene isomerization * organic-compounds * hindered rotation * methyl-groups * vaporization**Subject RIV**: BM - Solid Matter Physics ; Magnetism**Impact factor**: 2.045, year: 2013

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 (sigma(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 (sigma(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 sigma(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 sigma(r) to less than 1.5 % and 0.5 % at 300 K and 1000 K, respectively.

**Permanent Link:**http://hdl.handle.net/11104/0240648

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