Coupled Anharmonic Thermochemistry from Stratified Monte-Carlo Integration

This study presents CIMCI, a new semi-classical method for handling fully coupled anharmonicity in gas-phase thermodynamics that promises to be black-boxable, to be<br>applicable for all kinds of anharmonicity, and to scale better at higher dimensionality than other methods for handling gas-phase molecular anharmonicity. The method<br>does so by using automatically and recursively stratified, simultaneous Monte Carlo integration of multiple functions. For the small systems analyzed by this study, the<br>method’s anharmonic corrections match reference data better than those of other blackbox anharmonic methods, e.g. VPT2. This holds even when sampling with CIMCI<br>is done with primitive force fields, e.g. UFF, while the competing methods are used with proper, comprehensive potentials, e.g. the M06-2X meta-hybrid DFT functional.<br>With further refinements in Monte Carlo sampling efficiency, in the quality of fast potentials practical for Monte Carlo sampling, and in automatic detection of which stereoisomers should be included during sampling, CIMCI has the potential to be the ideal anharmonic treatment for larger molecules where the large number of conformers<br>and the high dimensionality of coupled torsions present major difficulties for other, existing treatments for anharmonicity.<br>

Coupled Anharmonic Thermochemistry from Stratified Monte-Carlo Integration

This study presents CIMCI, a new semi-classical method for handling fully coupled anharmonicity in gas-phase thermodynamics that promises to be black-boxable, to be<br>applicable for all kinds of anharmonicity, and to scale better at higher dimensionality than other methods for handling gas-phase molecular anharmonicity. The method<br>does so by using automatically and recursively stratified, simultaneous Monte Carlo integration of multiple functions. For the small systems analyzed by this study, the<br>method’s anharmonic corrections match reference data better than those of other blackbox anharmonic methods, e.g. VPT2. This holds even when sampling with CIMCI<br>is done with primitive force fields, e.g. UFF, while the competing methods are used with proper, comprehensive potentials, e.g. the M06-2X meta-hybrid DFT functional.<br>With further refinements in Monte Carlo sampling efficiency, in the quality of fast potentials practical for Monte Carlo sampling, and in automatic detection of which stereoisomers should be included during sampling, CIMCI has the potential to be the ideal anharmonic treatment for larger molecules where the large number of conformers<br>and the high dimensionality of coupled torsions present major difficulties for other, existing treatments for anharmonicity.<br>

A large-scale approach to modelling Biosignatures: First Steps

&lt;p&gt;For this poster I will be presenting the approaches taken to produce synthetic spectra for molecules believed to be biosignatures. In astrochemistry, biosignatures describe a group of molecules which could be produced by life and therefore act as an indication of it. Naturally, by being able to identify these molecules it will be possible to screen exoplanets for the possibility of harbouring life.&amp;#160;&lt;/p&gt; &lt;p&gt;Recently, Seager, Bains and Petkowski (2016) produced a catalogue of possible biosignatures, which totalled above 14,000 molecules. There are groups such as the ExoMol group which model these molecules at extremely high precision. However, due to the large number of molecules, a high precision method would take an unreasonable amount of time and therefore a faster means of producing spectra is required. The work shown within is designed to be quick and produce data for the full rovibronic spectrum rather than selected bands. I will show that anharmonic corrections are needed to be able to simulate qualitatively correct ro-vibrational transitions. In my method, this is done by implementing TOSH, transition optimised shifted hermites, which was first detailed by Lin, Gilbert and Gill (2007). Finally I will be presenting my latest results using this analytical anharmonic approach.&amp;#160;&lt;/p&gt;

Влияние термообработки на формирование активных центров меди, полученных путем взаимодействия хлорида меди с H-морденитом

The heat treatment effect on the formation of catalytically active copper centers obtained by solid-phase ion exchange between copper chloride and zeolite H-Mordenite was studied using X-ray absorption spectroscopy in the near edge (XANES) and extended (EXAFS) regions beyonds the copper K-edge. The spectra were measured in reaction conditions, at temperatures ranging from room temperature to 400°C. The analysis of the spectra performed by direct calculations of Cu K-XANES and Cu K-EXAFS fitting with account for anharmonic corrections showed that up to 200 ° C ion exchange does not occurs and copper remains in the state of CuCl. The heating above 200 ° C result in implantation of copper atom in zeolite framework.

Amino acetaldehyde conformers: structure and spectroscopic properties

ABSTRACT We present a computational study of the different conformers of amino acetaldehyde. This molecule is a precursor of glycine and also an isomer of the detected molecules acetaldehyde and methylformamide. In addition, a previous theoretical result shows that amino acetaldehyde could be formed from the gas phase reaction of formamide with CH$_{5}^{+}$. Different computational approaches, going from density functional theory (DFT) to coupled cluster (CC) calculations, are employed for the characterization of the amino acetaldehyde conformers. We locate four low-lying conformation on the singlet potential energy surface (PES), two with a synperiplanar arrangement of the carboxylic oxygen atom and the NH2 group, and the other two conformers with an anticlinal disposition. All levels of theory predict the conformer with a synperiplanar arrangement and the H atoms of the NH2 group pointing in the direction of the oxygen, denoted as in-sp-amino acetaldehyde, as the most stable. The viability of the interconversion processes between the four conformers in space is analysed. Relevant spectroscopic parameters to rotational spectroscopy with ‘spectroscopic’ accuracy at the composite level are reported. Vibrational frequencies and infrared intensities are also computed at the CC with single and double excitations (CCSD) level including anharmonic corrections. This information could help in the experimental characterization of amino acetaldehyde that could be considered as a good candidate molecule to be searched for in space.

The role of dispersion and anharmonic corrections in conformational analysis of flexible molecules: the allyl group rotamerization of matrix isolated safrole

Conformational changes of the monomeric safrole isolated in low temperature xenon matrices, induced thermally or using narrow-band UV radiation, represent challenging example for the theoretical structural, spectroscopic and energetic analysis.