17 research outputs found
Theoretical Study of the Ti-Cl Bond Cleavage Reaction in TiCl4
No full textIn this work the kinetics of the TiCl4 TiCl3 + Cl reaction is studied theoretically. A variable-reaction coordinate transition-state theory (VRC-TST) is used to calculate the high-pressure limit rate coefficients. The interaction energy surface for the VRC-TST step is sampled directly at the CASPT2(6e,4o)/cc-pVDZ level of theory including an approximate treatment of the spin-orbit coupling. The pressure-dependence of the reaction in an argon bath gas is explored using the master equation in conjunction with the optimised VRC-TST transition-state number of states. The collisional energy transfer parameters for the TiCl 4-Ar system are estimated via a "one-dimensional minimisation" method and classical trajectories. The Ti-Cl bond dissociation energy is computed using a complete basis set extrapolation technique with cc-pVQZ and cc-pV5Z basis sets. Good quantitative agreement between the estimated rate constants and available literature data is observed. However, the fall-off behaviour of the model results is not seen in the current experimental data. Sensitivity analysis shows that the fall-off effect is insensitive to the choice of model parameters and methods. More experimental work and development of higher-level theoretical methods are needed to further investigate this discrepancy
An assessment of the viability of alternatives to biodiesel transport fuels
No full textThis work presents an economic feasibility study of using algae and biochar burial strategies to offset carbon emission from the use of conventional fossil-derived transport fuels. The economic feasibility is quantified on the basis that the final price of the decarbonised fossil-derived diesel should be lower or equal to the price of biodiesel which is deemed to be the next best alternative. The extra costs associated with the carbon capture/offset via algae and biochar burial are estimated for the most typical scenarios using the economic models developed as part of this work. In addition, High Dimensional Model Representation based global sensitivity analyses are performed in order to quantify the influence of key model parameters on the overall costs. It was found that using algae burial to offset carbon emissions is not viable for principle reasons such as the amount of water required and the burial of phosphate as well as more than doubling the current diesel price. This price is mainly due to the high costs of pumping dilute algae slurry underground. The biochar burial approach, on the other hand, was found to be much more economically viable as it only increases the conventional diesel price by a small amount. This comparably low price is due to the revenue generated from selling the electricity produced from the pyrolysis by-products. In addition, the global sensitivity analysis revealed that the overall costs were the most sensitive to the wood price, as the wood feedstock may either be an income or an expenditure.National Research Foundation (NRF)Accepted versionThis research is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its CREATE programme
Automated Rational Design of Metal-Organic Polyhedra.
No full textMetal-organic polyhedra (MOPs) are hybrid organic-inorganic nanomolecules, whose rational design depends on harmonious consideration of chemical complementarity and spatial compatibility between two or more types of chemical building units (CBUs). In this work, we apply knowledge engineering technology to automate the derivation of MOP formulations based on existing knowledge. For this purpose we have (i) curated relevant MOP and CBU data; (ii) developed an assembly model concept that embeds rules in the MOP construction; (iii) developed an OntoMOPs ontology that defines MOPs and their key properties; (iv) input agents that populate The World Avatar (TWA) knowledge graph; and (v) input agents that, using information from TWA, derive a list of new constructible MOPs. Our result provides rapid and automated instantiation of MOPs in TWA and unveils the immediate chemical space of known MOPs, thus shedding light on new MOP targets for future investigations
First-Principles Thermochemistry for the Thermal Decomposition of Titanium Tetraisopropoxide
No full textThe thermal decomposition of titanium
tetraisopropoxide (TTIP)
is investigated using quantum chemistry, statistical thermodynamics,
and equilibrium composition analysis. A set of 981 Ti-containing candidate
species are proposed systematically on the basis of the thermal breakage
of bonds within a TTIP molecule. The ground state geometry, vibrational
frequencies and hindrance potentials are calculated for each species
at the B97-1/6-311+G(d,p) level of theory. Thermochemical data are
computed by applying statistical thermodynamics and, if unknown, the
standard enthalpy of formation is estimated using balanced reactions.
Equilibrium composition calculations are performed under typical combustion
conditions for premixed flames. The thermodynamically stable decomposition
products for different fuel mixtures are identified. A strong positive
correlation is found between the mole fractions of Ti species containing
carbon and the TTIP precursor concentration
First-Principles Thermochemistry for the Thermal Decomposition of Titanium Tetraisopropoxide
No full textThe thermal decomposition of titanium
tetraisopropoxide (TTIP)
is investigated using quantum chemistry, statistical thermodynamics,
and equilibrium composition analysis. A set of 981 Ti-containing candidate
species are proposed systematically on the basis of the thermal breakage
of bonds within a TTIP molecule. The ground state geometry, vibrational
frequencies and hindrance potentials are calculated for each species
at the B97-1/6-311+G(d,p) level of theory. Thermochemical data are
computed by applying statistical thermodynamics and, if unknown, the
standard enthalpy of formation is estimated using balanced reactions.
Equilibrium composition calculations are performed under typical combustion
conditions for premixed flames. The thermodynamically stable decomposition
products for different fuel mixtures are identified. A strong positive
correlation is found between the mole fractions of Ti species containing
carbon and the TTIP precursor concentration
First-Principles Thermochemistry for the Thermal Decomposition of Titanium Tetraisopropoxide
No full textThe thermal decomposition of titanium
tetraisopropoxide (TTIP)
is investigated using quantum chemistry, statistical thermodynamics,
and equilibrium composition analysis. A set of 981 Ti-containing candidate
species are proposed systematically on the basis of the thermal breakage
of bonds within a TTIP molecule. The ground state geometry, vibrational
frequencies and hindrance potentials are calculated for each species
at the B97-1/6-311+G(d,p) level of theory. Thermochemical data are
computed by applying statistical thermodynamics and, if unknown, the
standard enthalpy of formation is estimated using balanced reactions.
Equilibrium composition calculations are performed under typical combustion
conditions for premixed flames. The thermodynamically stable decomposition
products for different fuel mixtures are identified. A strong positive
correlation is found between the mole fractions of Ti species containing
carbon and the TTIP precursor concentration
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An Ontology and Semantic Web Service for Quantum Chemistry Calculations.
No full textThe purpose of this article is to present an ontology, termed OntoCompChem, for quantum chemistry calculations as performed by the Gaussian quantum chemistry software, as well as a semantic web service named MolHub. The OntoCompChem ontology has been developed based on the semantics of concepts specified in the CompChem convention of Chemical Markup Language (CML) and by extending the Gainesville Core (GNVC) ontology. MolHub is developed in order to establish semantic interoperability between different tools used in quantum chemistry and thermochemistry calculations, and as such is integrated into the J-Park Simulator (JPS)-a multidomain interactive simulation platform and expert system. It uses the OntoCompChem ontology and implements a formal language based on propositional logic as a part of its query engine, which verifies satisfiability through reasoning. This paper also presents a NASA polynomial use-case scenario to demonstrate semantic interoperability between Gaussian and a tool for thermodynamic data calculations within MolHub
Question answering system for chemistry—a semantic agent extension
No full textThis paper introduces an extension of a previously developed question answering (QA) system for chemistry, operating on a knowledge graph (KG) called Marie. This extension enables the automatic invocation of semantic agents to answer questions when static data is absent from the KG. The agents are semantically described using the agent ontology, OntoAgent, to enable automated agent discovery and invocation. The natural language processing (NLP) models of the QA system need to be trained in order to interpret questions to be answered by new agents. For this purpose, we extend OntoAgent so that it becomes possible to automatically create training material for the NLP models. We evaluate the extended QA system with two example chemistry-related agents and an evaluation question set. The evaluation result shows that the extension allows the QA system to discover the suitable agent and to invoke the agent by automatically constructing requests from the semantic agent description, thereby increasing the range of questions the QA system can answer.National Research Foundation (NRF)Published versionThis project is funded by the National Research Foundation (NRF), Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme. Part of this work was supported by Towards Turing 2.0 under the EPSRC Grant EP/W037211/1 and The Alan Turing Institute. M.K. gratefully acknowledges the support of the Alexander von Humboldt Foundation. X. Zhou acknowledges financial support provided CMCL Innovations
An Ontology and Semantic Web Service for Quantum Chemistry Calculations
No full textThe purpose of this
article is to present an ontology, termed OntoCompChem,
for quantum chemistry calculations as performed by the Gaussian quantum
chemistry software, as well as a semantic web service named MolHub.
The OntoCompChem ontology has been developed based on the semantics
of concepts specified in the CompChem convention of Chemical Markup
Language (CML) and by extending the Gainesville Core (GNVC) ontology.
MolHub is developed in order to establish semantic interoperability
between different tools used in quantum chemistry and thermochemistry
calculations, and as such is integrated into the J-Park Simulator
(JPS)a multidomain interactive simulation platform and expert
system. It uses the OntoCompChem ontology and implements a formal
language based on propositional logic as a part of its query engine,
which verifies satisfiability through reasoning. This paper also presents
a NASA polynomial use-case scenario to demonstrate semantic interoperability
between Gaussian and a tool for thermodynamic data calculations within
MolHub
OntoPESScan: An Ontology for Potential Energy Surface Scans
No full textIn this work, a new OntoPESScan ontology is developed for the semantic representation of one-dimensional potential energy surface (PES) scans, a central concept in computational chemistry. This ontology is developed in line with knowledge graph principles and The World Avatar (TWA) project. OntoPESScan is linked to other ontologies for chemistry in TWA, including OntoSpecies, which helps uniquely identify species along the PES and access their properties, and OntoCompChem, which allows association of potential energy surfaces with the quantum chemical calculations and concepts used to derive them. A forcefield fitting agent is also developed that makes use of the information in the OntoPESScan ontology to fit force fields to reactive surfaces of interest on the fly by making use of the empirical valence bond methodology. This agent is demonstrated to successfully parametrise two cases, a PES scan on ethanol, and a PES scan on a localized π-radical PAH hypothesized to play a role in soot formation during combustion. OntoPESScan is an extension to the capabilities of TWA, and in conjunction with potential further ontological support for molecular dynamics and reactions, will further progress towards an open, continuous, and self-growing knowledge graph for chemistry
