All Hands on Deck: Accelerating Ab Initio Thermochemistry via Wavefunction Approximations

<div>We accelerate the G4(MP2) composite model by fine-tuning the individual steps using resolution-of-identity and domain‐based local pair‐natural orbitals. The new variant, G4(MP2)-XP, has a low prediction error when tested on 1694 benchmark molecules. To showcase the method's relevance for large molecules, we determine and present a new reference value for the standard formation enthalpy of buckminsterfullerene. We expect G4(MP2)-XP to become the <i>de facto</i> method for rapid and accurate production of thermochemistry big data.</div>

All Hands on Deck: Accelerating Ab Initio Thermochemistry via Wavefunction Approximations

<div>We accelerate the G4(MP2) composite model by fine-tuning the individual steps using resolution-of-identity and domain‐based local pair‐natural orbitals. The new variant, G4(MP2)-XP, has a low prediction error when tested on 1694 benchmark molecules. To showcase the method's relevance for large molecules, we determine and present a new reference value for the standard formation enthalpy of buckminsterfullerene. We expect G4(MP2)-XP to become the <i>de facto</i> method for rapid and accurate production of thermochemistry big data.</div>

Calorimetric Studies of Magnesium-Rich Mg-Pd Alloys

Solution calorimetry with liquid aluminum as the bath was conducted to measure the enthalpy of a solution of magnesium and palladium as well as the standard formation enthalpies of selected magnesium-palladium alloys. These alloys were synthesized from pure elements, which were melted in a resistance furnace that was placed in a glove box containing high-purity argon and a very low concentration of impurities, such as oxygen and water vapor. A Setaram MHTC 96 Line evo drop calorimeter was used to determine the energetic effects of the solution. The enthalpies of the Mg and Pd solutions in liquid aluminum were measured at 1033 K, and they equaled −8.6 ± 1.1 and −186.8 ± 1.1 kJ/mol, respectively. The values of the standard formation enthalpy of the investigated alloys with concentrations close to the Mg6Pd, ε, Mg5Pd2, and Mg2Pd intermetallic phases were determined as follows: −28.0 ± 1.2 kJ/mol of atoms, −32.6 ± 1.6 kJ/mol of atoms, −46.8 ± 1.4 kJ/mol of atoms, and −56.0 ± 1.6 kJ/mol of atoms, respectively. The latter data were compared with existing experimental and theoretical data from the literature along with data calculated using the Miedema model.

Thermodynamic Characteristics of a Series of Antimony Compounds: Standard Formation Enthalpy of Antimony Oxychloride SbOCl

The present work opens a series of publications devoted to the description of the results of determination or clarification of the formation enthalpies of certain antimony compounds that are of significant applied interest to science and technology. The measurement results of enthalpy of interaction crystalline SbCl3 and water with formation of crystalline SbOCl are given. On the basis of the obtained and literature data, the value of standard formation enthalpy of the product of this interaction --- antimony oxychloride SbOCl at temperature 298.15 K is calculated. This value coincided with the reference values within the margin of error. An attempt was made to determine the dissolution enthalpy of SbCl3 in a two-molar aqueous solution of hydrochloric acid: the obtained approximate value of this characteristic was --30 ± 2 kJ/mol

Correlation model to estimate the thermodynamic properties

A technique for constructing the correlation dependencies of the thermodynamic properties of similar compounds was proposed. This technique is based on the Taylor expansion in the supposed analytic relationship between properties. The constructed correlation dependencies were used to estimate the thermodynamic properties of the condensed bromides and iodides of hafnium HfGn (G [Formula: see text] Br, I and [Formula: see text], 2, 3, 4) and the compounds formed in the PbO–SiO2 system. Standard formation enthalpy [Formula: see text], entropy [Formula: see text], heat capacity [Formula: see text] and temperature dependencies [Formula: see text] at temperatures T[Formula: see text][Formula: see text]k to 3000[Formula: see text]k were estimated. The standard estimation error of the thermodynamic properties of the compounds in the PbO–SiO2 system does not exceed 2% for all the estimated properties. For condensed halides, the standard estimation error was (1) [Formula: see text]% for enthalpy, (2) [Formula: see text]% for entropy, (3) [Formula: see text]% for heat capacity.

QUANTUM-CHEMICAL PREDICTION OF FORMATION ENTHALPY OF CYCLOALKANE

Based on the s-homodesmotic model and the seven different density functional theory (DFT) methods, we calculate standard formation enthalpy of cycloalkane of up to 10 carbons. Among the 21 different combinations, the scheme using MPWB1K method and working reactions when s = 2 achieves the experimental accuracy with RMSD of 8.49 kJ/mol. Also, credibility of this scheme is proved by discussion on influence from different aspects.