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

Abstract

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

Fast and Accurate Estimation of Gas-Phase Entropy from the Molecular Surface Curvature

“…[14][15][16] Density functional theory with different functionals and basis sets has been frequently employed in these calculations. 17,18 Other methods based on semi-empirical orbital theory 15,19 and molecular dynamics simulations [20][21][22] have also been used to estimate entropies. Many of these methods however, require considerable time and computational resources, and are therefore not suitable for applications where millions or billions of such calculations are required, such as in virtual screening for drug discovery.…”

Fast and Accurate Estimation of Gas-Phase Entropy from the Molecular Surface Curvature

“…[16][17][18] These studies have frequently made use of different functionals and basis sets. 19,20 Other methods based on semi-empirical orbital theory 17,21 and molecular dynamics simulations [22][23][24] have also been used to estimate entropies. Many of these methods however, require considerable time and computational resources, and are therefore not suitable for applications where millions or billions of such calculations are required, such as in virtual screening for drug discovery.…”

Unknown Knowns: Case Studies in Uncertainties in the Computation of Thermochemical Parameters

“…A more limited approach was used byČervinka et al in analysing 5,6 the uncertainties resulting from using a one-dimensional hindered rotor (HR) model for a set of 60 closed shell molecules; they found that errors of 20% in the HR contribution to the entropy and of 5%…”