RESUMEN

Composite methods are the combination of ab initio calculations used to achieve high precision in the face of a computational reduction. Weizmann-n theories (n = 1, 2, 3, and 4) stand out for presenting a high precision, and a version of the W1 theory is the W1BD theory that uses ab initio Brueckner Doubles (BD) methods. One way to reduce the computational cost of composite methods and maintain accuracy is to use pseudopotentials in the calculation steps; in this context, W1BDCEP composite method was developed from the respective W1BD all-electron version by considering the implementation of compact effective pseudopotential (CEP). The test set used to evaluate the theory were 8 proton affinities (PA0), 46 electron affinities (EA0), 54 ionization energies (IE0), 80 enthalpies of formation (ΔfH0), and 10 bond dissociation energies (BDE). The mean absolute deviation values (MADs) for W1BD and for the version adapted to the pseudopotential, W1BDCEP, were similar, with values of 0.97 kcal mol-1 and 1.03 kcal mol-1, respectively, when the properties PA0, EA0, IE0, and ΔfH0 were evaluated together. Comparing the versions of the theories that employ ab initio Brueckner Doubles calculations with the W1 and W1CEP theories, it is possible to observe that the W1BD and W1BDCEP theories are more accurate than the W1 theory (MADW1 = 1.25 kcal mol-1) and W1CEP (MADW1CEP = 1.44 kcal mol-1), proving the accuracy of using the BD method. Pseudopotential reduces computational time by up to 30% and thus enables more accurate calculations with less computational time.

RESUMEN

The ThermoML Archive is a subset of Thermodynamics Research Center (TRC) data holdings corresponding to cooperation between NIST TRC and five journals: Journal of Chemical Engineering and Data (ISSN: 1520-5134), The Journal of Chemical Thermodynamics (ISSN: 1096-3626), Fluid Phase Equilibria (ISSN: 0378-3812), Thermochimica Acta (ISSN: 0040-6031), and International Journal of Thermophysics (ISSN: 1572-9567). Data from initial cooperation (around 2003) through the 2019 calendar year are included. The archive has undergone a major update with the goal of improving the FAIRness and user experience of the data provided by the service. The web application provides comprehensive property browsing and searching capabilities; searching relies on a RESTful API provided by the Cordra software for managing digital objects. JSON files with a schema derived from ThermoML are provided as an additional serialization to lower the barrier to programmatic consumption of the information, for stakeholders who may have a preference of JSON over XML. The ThermoML and JSON files for all available entries can be downloaded from data.nist.gov (https://data.nist.gov/od/id/mds2-2422).

Asunto(s)

Programas Informáticos

RESUMEN

Scientific projects frequently involve measurements of thermophysical, thermochemical, and other related properties of chemical compounds and materials. These measured property data have significant potential value for the scientific community, but incomplete and inaccurate reporting often hampers their utilization. The present IUPAC Technical Report summarizes the needs of chemical engineers and researchers as consumers of these data and shows how publishing practices can improve information transfer. In the Report, general principles of Good Reporting Practice are developed together with examples illustrating typical cases of reporting issues. Adoption of these principles will improve the quality, reproducibility, and usefulness of experimental data, bring a better level of consistency to results, and increase the efficiency and impact of research. Closely related to Good Reporting Practice, basic elements of Good Research Practice are also introduced with a goal to reduce the number of ambiguities and unresolved problems within the thermophysical property data domain.

RESUMEN

The structures and thermodynamic properties of microhydrates of caesium metaborate (CsBO2) of nuclear safety interest are reported in this work. CsBO2 + n H2O (n = 1-4) molecular complexes were identified on the potential energy surface. The structures were optimized using the ωB97XD DFT method and the aug-cc-pVTZ basis set. Single-point energies were calculated at the CCSD(T)-F12a/awCVTZ and the ωB97XD/aug-cc-pVQZ levels of theory. The standard reaction enthalpies and the standard Gibbs free reaction energies were reported for all molecular complexes. The temperature dependence of ΔrG°(T) was evaluated for all studied structures over the temperature range 300-2000 K. Total hydration reactions were investigated. The results showed that the mono-hydrated form of CsBO2 exists only at temperatures lower than 720 K under standard conditions. The influence on the thermodynamic properties of the number of water molecules in the clusters was described, with successive dehydration from 720 to 480 K. In nuclear severe accident conditions, gaseous CsBO2 will remain unhydrated in the reactor coolant system.

RESUMEN

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) being soft ionization technique, has become a method of choice for high-throughput analysis of proteins and peptides. In this study, we have explored the potential of atypical anti-psychotic drug olanzapine (OLZ) as a matrix for MALDI-MS analysis of peptides aided with the theoretical studies. Seven small peptides were employed as target analytes to check performance of olanzapine and compared with conventional MALDI matrix α-cyano-4-hydroxycinnamic acid (HCCA). All peptides were successfully detected when olanzapine was used as a matrix. Moreover, peptides angiotensin Ι and angiotensin ΙΙ were detected with better S/N ratio and resolution with this method as compared to their analysis by HCCA. Computational studies were performed to determine the thermochemical properties of olanzapine in order to further evaluate its similarity to MALDI matrices which were found in good agreement with the data of existing MALDI matrices.

Asunto(s)

Benzodiazepinas/química , Rayos Láser , Espectrometría de Masa por Láser de Matriz Asistida de Ionización Desorción/métodos , Rayos Ultravioleta , Animales , Sitios de Unión , Calibración , Ácidos Cumáricos/química , Modelos Químicos , Conformación Molecular , Peso Molecular , Olanzapina , Péptidos/química , Protones , Programas Informáticos , Porcinos , Temperatura

RESUMEN

Molecular crystals expand appreciably upon heating due to both zero-point and thermal vibrational motion, yet this expansion is often neglected in molecular crystal modeling studies. Here, a quasi-harmonic approximation is coupled with fragment-based hybrid many-body interaction calculations to predict thermal expansion and finite-temperature thermochemical properties in crystalline carbon dioxide, ice Ih, acetic acid and imidazole. Fragment-based second-order Möller-Plesset perturbation theory (MP2) and coupled cluster theory with singles, doubles and perturbative triples [CCSD(T)] predict the thermal expansion and the temperature dependence of the enthalpies, entropies and Gibbs free energies of sublimation in good agreement with experiment. The errors introduced by neglecting thermal expansion in the enthalpy and entropy cancel somewhat in the Gibbs free energy. The resulting ∼ 1-2 kJ mol(-1) errors in the free energy near room temperature are comparable to or smaller than the errors expected from the electronic structure treatment, but they may be sufficiently large to affect free-energy rankings among energetically close polymorphs.

RESUMEN

The partial and integral enthalpy of mixing of molten ternary Co-Sb-Sn alloys was determined performing high temperature drop calorimetry in a large compositional range at 1273 K. Measurements have been done along five sections, xSb/xSn ≈ 1:1, xSb/xSn ≈ 1:3, xSb/xSn ≈ 3:1, xCo/xSn ≈ 1:4, and xCo/xSb ≈ 1:5. Additionally, binary alloys of the constituent systems Co-Sb and Co-Sn were investigated at the same temperature. All the binary data were evaluated by means of a standard Redlich-Kister polynomial fit whereas ternary data were fitted on the basis of an extended Redlich-Kister-Muggianu model for substitutional solutions. An iso-enthalpy plot of the ternary system was constructed. In addition, the extrapolation Model of Toop was applied and compared to our data.