State-of-the-Art Calculations of Sublimation Enthalpies for Selected Molecular Crystals and Their Computational Uncertainty

Abstract

A computational methodology for calculation of sublimation enthalpies of molecular crystals from first principles is developed and validated by comparison to critically evaluated literature experimental data. Temperature-dependent sublimation enthalpies for a set of selected 22 molecular crystals in their low-temperature phases are calculated. The computational methodology consists of several building blocks based on high-level electronic structure methods of quantum chemistry and statistical thermodynamics. Ab initio methods up to the coupled clusters with iterative treatment of single and double excitations and perturbative triples correction with an estimated complete basis set description [CCSD(T)/CBS] are used to calculate the cohesive energies of crystalline phases within a fragment-based additive scheme. Density functional theory (DFT) calculations with periodic boundary conditions (PBC) coupled with the quasi-harmonic approximation are used to evaluate the thermal contributions to the enthalpy of the solid phase. The properties of the vapor phase are calculated within the ideal-gas model using the rigid-rotor harmonic-oscillator model with correction for internal rotation using a one-dimensional hindered rotor approximation and a proper treatment of the molecular rotational degrees of freedom in the vicinity of 0 K. All individual terms contributing to the sublimation enthalpy as a function of temperature are discussed and their uncertainties estimated by comparison to critically evaluated experimental data.

Molecular Simulations of Thermodynamic Properties for the Systemα‐Cyclodextrin/Alcohol in Aqueous Solution

“…Finally it is noted that if the assumption that all activity coefficients are unity proves to be unrealistic, finite concentration activity coefficients may also be obtained from molecular dynamics free-energy calculations [57]. For saturated solutions of solid solutes the need to calculate the residual chemical potential of the solid hampers the use of molecular simulations [58]. However, molecular dynamics simulations can straightforwardly be used to calculate relative solubilities for the same solute in different solvents [20].…”

Impact of dihydrogen bonding on lattice energies and sublimation enthalpies of crystalline [H2GaNH2]3, [H2BNH2]3 and [H2GeCH2]3

“…For molecular solids, lattice energy, the energy per molecule required to separate the molecules to gas-phase species, is the major contributor to the value of DH sub , and there has been much effort focused on using computational methods to predict DH sub . [1][2][3][4][5][6][7][8][9][10] Lattice energy depends on the strength of intermolecular bonds present in the crystalline phase and there has been great interest in structures exhibiting dihydrogen bonds. Ammoniaborane and related compounds, including [H 2 BNH 2 ] 3 , exhibit intermolecular dihydrogen bonds and have been the focus of study due to their potential application in hydrogen storage systems.…”

Ab initiothermodynamic properties and their uncertainties for crystalline α-methanol

“…Most computational studies of molecular crystals neglect thermal contributions to thermochemical properties at finite temperatures and pressures, since calculating static cohesive electronic energies is much simpler than rigorously accounting for all relevant vibrational and thermal terms. However, predicting the most stable phase or polymorph under certain thermodynamic conditions can require sub-kJ mol À1 accuracy, 2,3 in which case factors such as thermal expansion of the crystal and the temperature dependence of the isobaric heat capacity can play a key role. These effects can be captured only if the anharmonicity of the unit cell vibrations is included in the computational model.…”

“…Several recent studies and reviews employ the quasi-harmonic approximation to calculate the thermodynamic properties of molecular crystals and emphasize the importance of the thermal terms for phenomena such as the thermal expansivity or polymorphism. 2,3,[17][18][19] The results of those studies indicate that the quasi-harmonic approximation sometimes enables calculation of temperature-dependent trends in properties such as molar volumes, sublimation enthalpies, or Gibbs energies for various molecular crystals with a semi-quantitative accuracy or better. This sometimes translates to sub-kJ mol À1 accuracy, which is important for polymorph stability ranking [18][19][20] and predicting of phase change properties.…”

“…This sometimes translates to sub-kJ mol À1 accuracy, which is important for polymorph stability ranking [18][19][20] and predicting of phase change properties. 3,12,21 Quasi-harmonic models are also capable of capturing anomalous behavior such as the negative thermal expansion of some systems 2,4 or nonmonotonic sublimation enthalpy trends, 3,12 although several cases have been reported where the computational methodology fails to reproduce experimental data. 22 Other limitations of the quasi-harmonic approximation arise from the high computational cost for large molecules/unit cells, flexible molecules, and other cases where such high accuracy cannot practically be achieved.…”