Two Faces of the Two-Phase Thermodynamic Model

Abstract

The quantum harmonic model and the two-phase thermodynamic method (2PT) are widely used to obtain quantumcorrected properties such as isobaric heat capacities or molar entropies. 2PT heat capacities were calculated inconsistently in the literature. For water, the classical heat capacity was also considered, but for organic liquids, it was omitted. We reanalyzed the performance of different quantum corrections on the heat capacities of common organic solvents against experimental data. We have pointed out serious flaws in previous 2PT studies. The vibrational density of states was calculated incorrectly causing a 39% relative error in diffusion coefficients and 45% error in the 2PT heat capacities. The wrong conversion of isobaric and isochoric heat capacities also caused about 40% error but in the other direction. We have introduced the concept of anharmonic correction (AC), which is simply the deviation of the classical heat capacity from that of the harmonic oscillator model. This anharmonic contribution is around +30 to 40 J/(mol K) for water depending on the water model and −8 to −10 J/(mol K) for hydrocarbons and halocarbons. AC is unrealistically large, +40 J/(K mol) for alcohols and amines, indicating some deficiency of the OPLS force field. The accuracy of the computations was also assessed with the determination of the self-diffusion coefficients.

2-in-1 Phase Space Sampling for Calculating the Absorption Spectrum of the Hydrated Electron

“…The quantized properties can be readily computed from the filtered trajectories. GSTA was successfully applied to different water phases to analyze dynamic and structural properties. , The heat capacities of 100 organic liquids were also computed, and the results also validated the GSTA method . NQEs were investigated by the GSTA method in the UV–vis absorption spectrum of two acridine derivatives .…”

“… 53 , 55 The heat capacities of 100 organic liquids were also computed, and the results also validated the GSTA method. 56 NQEs were investigated by the GSTA method in the UV–vis absorption spectrum of two acridine derivatives. 57 The spectrum was computed as an average from hundreds of structures taken from AIMD simulations.…”

Thermodynamics of supercritical carbon dioxide mixtures across the Widom line

“…For the enthalpy, isobaric heat capacity and speed of sound, ideal contributions from the reference EOS (see Sec. may be questioned due to the missing internal degrees of freedom of the employed molecular models 75 . However, the comparison of the residual isobaric heat capacity from simulation and EOS shows good agreement, suggesting a small influence of the internal degrees of freedom on the studied properties.…”

2-in-1 Phase Space Sampling for Calculating the Absorption Spectrum of the Hydrated Electron

“…53,55 The heat capacities of 100 organics liquids were also computed, and the results also validated the GSTA method. 56 NQEs were investigated by the GSTA method in the UV-VIS absorption spectrum of two acridine derivatives. 57 The spectrum was computed as an average from hundreds of structures taken from ab initio molecular dynamics simulations.…”