Obtaining the lattice energy of the anthracene crystal by modern yet affordable first-principles methods

The non-covalent interactions in organic molecules are known to drive their self-assembly to form molecular crystals. We compare, in the case of anthracene and against experimental (electronic-only) sublimation energy, how modern quantum-chemical methods are able to calculate this cohesive energy taking into account all the interactions between occurring dimers in both first-and second-shells. These include both O(N 6)- and O(N 5)-scaling methods, Local Pair Natural Orbital-parameterized Coupled-Cluster Single and Double, and Spin-Component-Scaled-Møller-Plesset perturbation theory at second-order, respectively, as well as the most modern family of conceived density functionals: double-hybrid expressions in several variants (B2-PLYP, mPW2-PLYP, PWPB95) with customized dispersion corrections (–D3 and –NL). All-in-all, it is shown that these methods behave very accurately producing errors in the 1–2 kJ/mol range with respect to the experimental value taken into account the experimental uncertainty. These methods are thus confirmed as excellent tools for studying all kinds of interactions in chemical systems.Financial support by the “Ministerio de Economía y Competitividad” of Spain and the “European Regional Development Fund” through projects CTQ2011-27253, CTQ2012-31914, and Consolider-Ingenio CSD2007-00010 in Molecular Nanoscience, and by the Generalitat Valenciana (ISIC 2012/008 and PROMETEO/2012/053) is acknowledged. The work in Mons is supported by the Belgian National Fund for Scientific Research (FNRS). Y.O. is a FNRS Post-doctoral Research Fellow. J.C.S.G. is a FNRS Visiting Professor

A thermochemical and theoretical study of the phenylpyridine isomers

The standard (p° = 0.1 MPa) molar enthalpies of formation for 2-, 3-, and 4-phenylpyridine in the gas phase were derived from the standard molar enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpies of vaporization for 2-, 3-, and 4-phenylpyridine at T = 298.15 K were measured by correlation-gas chromatography. The enthalpy of sublimation of 4-phenylpyridine was obtained as a weighted mean of the value derived from the vaporization and fusion enthalpy values and the value measured directly by Calvet microcalorimetry. The following enthalpies of formation were then derived:  2-phenylpyridine, g = 228.3 ± 5.8 kJ·mol-1; 3-phenylpyridine, g = 240.9 ± 5.5 kJ·mol-1; 4-phenylpyridine, g = 240.0 ± 3.3 kJ·mol-1. The most stable geometries of all phenylpyridine isomers were obtained using both restricted Hartree−Fock (RHF) and density functional theory (DFT/B3LYP) methods. The resulting geometries were then used to obtain estimates of enthalpies of formation of the three isomers of phenylpyridine, which are in good agreement with the experimental values. A theoretical interpretation of the effect of the phenyl ring has on the relative stabilities of the three molecules is presented

van der Waals density functional calculations of binding in molecular crystals

A recent paper [J. Chem. Phys. 132, 134705 (2010)] illustrated the potential of the van der Waals density functional (vdW-DF) method [Phys. Rev. Lett. 92, 246401 (2004)] for efficient first-principle accounts of structure and cohesion in molecular crystals. Since then, modifications of the original vdW-DF version (identified as vdW-DF1) has been proposed, and there is also a new version called vdW-DF2 [ArXiv 1003.5255], within the vdW-DF framework. Here we investigate the performance and nature of the modifications and the new version for the binding of a set of simple molecular crystals: hexamine, dodecahedrane, C60, and graphite. These extended systems provide benchmarks for computational methods dealing with sparse matter. We show that a previously documented enhancement of non-local correlations of vdW-DF1 over an asymptotic atom-based account close to and a few A, beyond binding separation persists in vdW-DF2. The calculation and analysis of the binding in molecular crystals requires appropriate computational tools. In this paper, we also present details on our real-space parallel implementation of the vdW-DF correlation and on the method used to generate asymptotic atom-based pair potentials based on vdW-DF.Comment: 5 pages, 4 figure

General method for prediction of thermal conductivity for well-characterized hydrocarbon mixtures and fuels up to extreme conditions using entropy scaling

A general and efficient technique is developed to predict the thermal conductivity of well-characterized hydrocarbon mixtures, rocket propellant (RP) fuels, and jet fuels up to high temperatures and high pressures (HTHP). The technique is based upon entropy scaling using the group contribution method coupled with the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state. The mixture number averaged molecular weight and hydrogen to carbon ratio are used to define a single pseudo-component to represent the compounds in a well-characterized hydrocarbon mixture or fuel. With these two input parameters, thermal conductivity predictions are less accurate when the mixture contains significant amounts of iso-alkanes, but the predictions improve when a single thermal conductivity data point at a reference condition is used to fit one model parameter. For eleven binary mixtures and three ternary mixtures at conditions from 288 to 360 K and up to 4,500 bar, thermal conductivities are predicted with mean absolute percent deviations (MAPDs) of 16.0 and 3.0% using the two-parameter and three-parameter models, respectively. Thermal conductivities are predicted for three RP fuels and three jet fuels at conditions from 293 to 598 K and up to 700 bar with MAPDs of 14.3 and 2.0% using the two-parameter and three-parameter models, respectively

Herringbone Pattern and CH–π Bonding in the Crystal Architecture of Linear Polycyclic Aromatic Hydrocarbons

The herringbone pattern is a pervasive structural motive found in most molecular crystals involving aromatic compounds. A plot of the experimental sublimation enthalpies of members of increasing size of the acene, phenacene and p-phenyl families versus the number of carbons uncovers a linear relationship between the two magnitudes, suggesting a major role of CH–π bonding. In this work we undertake the task of evaluating the relevance of the edge-to-face interaction (or CH–π bond) in the overall reticular energy of the crystal, to quantitatively assess the importance of this structural element. Following a heuristic approach, we considered the series of acenes, phenacenes and p-phenyls and analyzed the edge-to-face interaction between the molecules as they occur in the experimental crystal network. Isolation of the relevant molecular dimers allows to incorporate some of the most sophisticated tools of quantum chemistry and get a reliable picture of the isolated bond. When compared to the experimental sublimation energy, our results are conclusive: this sole interaction is the largest contribution to the lattice energy, and definitively dictates the crystal architecture in all the studied cases. Elusive enough, the edge-to-face interaction is mainly dominated by correlation interactions, specifically in the form of dispersion and, to a less extent, of charge-transfer terms. A suggestive picture of the bond has been obtained by displaying the differences in local electron densities calculated by either correlated or non-correlated methods.Financial support by the spanish “Ministerio de Ciencia e Innovación MICINN” (grants CTQ2011-24165, FIS2012-33521 and FIS2012-35880) and the Universidad de Alicante is gratefully acknowledged. We also acknowledge support from the DGUI of the Comunidad de Madrid under the R&D Program of activities MODELICO-CM/S2009ESP-1691

Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds. Sublimation, Vaporization and Fusion Enthalpies From 1880 to 2010

Article on phase transition enthalpy measurements of organic and organometallic compounds, sublimation, and vaporization and fusion enthalpies from 1880 to 2010

Enthalpies of Sublimation of Organic and Organometallic Compounds. 1910–2001

Article on enthalpies of sublimation of organic and organometallic compounds