1,727,732 research outputs found
60th Symposium on Theoretical Chemistry: Next-Generation Theoretical Chemistry
Full text linkThis year’s Symposium for Theoretical Chemistry (STC 2024) took place in Braunschweig at the beginning of September 2024. The Symposium for Theoretical Chemistry is the most important international conference for theoretical chemistry in the German-speaking countries and takes place annually at different locations in Germany, Austria or Switzerland. This year, almost 400 participants came to TU Braunschweig for this event. The conference was organized by Christoph Jacob and Jonny Proppe (TU Braunschweig). This year’s conference was held under the motto “Next-Generation Theoretical Chemistry”. Accordingly, STC 2024 celebrated both established and emerging fields in theoretical chemistry, including electronic structure theory, molecular dynamics, quantum computing, artificial intelligence, and uncertainty quantification. In doing so, it particularly featured young scientist working on diverse topics in theoretical chemistry
Atoms in Valence Bond – AiVB : synopsis and test results
No full textThe Atoms in Valence Bond (AiVB) method, a new approach in the Valence Bond, is introduced. This approach combines the ideas behind the early Atoms in Molecules (AIM) developments, e.g. by Moffit [21], to understand a molecular wave function in terms of proper atomic wave functions, with the available framework of the VBSCF [17,18] as implemented in TURTLE [19]. The fundamental theoretical tools, to explain the AiVB concept, are shown and the initial test results are presented
Theoretical chemistry: current applications to photochemistry and thermochemistry
No full textA historical perspective is given contrasting challenges and advances in theoretical chemistry at the time the first issue of Theoretical Chemistry Accounts appeared in 1962 and the progress achieved since then as expressed in current state-of-the-art applications in photochemistry and thermochemistry
Generation of Kekule valence structures and the corresponding valence bond wave function
No full textA new scheme, called “list of nonredundant bonds”, is presented to record the number of bonds and their positions for the atoms involved in Kekulé valence structures of (poly)cyclic conjugated systems. Based on this scheme, a recursive algorithm for generating Kekulé valence structures has been developed and implemented. The method is general and applicable for all kinds of (poly)cyclic conjugated systems including fullerenes. The application of the algorithm in generating Valence Bond (VB) wave functions, in terms of Kekulé valence structures, is discussed and illustrated in actual VB calculations. Two types of VBSCF calculations, one involving Kekulé valence structures only and the second one involving all covalent VB structures, were performed for benzene, pentalene, benzocyclobutadiene, and naphthalene. Both strictly local and delocalised p-orbitals were used in these calculations. Our results show that, when the orbitals are restricted to their own atoms, other VB structures (Dewar structures) also have a significant contribution in the VB wave function. When removing this restriction, the other VB structures (Dewar and also the ionic structures) are accommodated in the Kekulé valence structures, automatically. Therefore, at VBSCF delocal level, the ground states of these systems can be described almost quantitatively by considering Kekulé valence structures only at a considerable saving of time
Delocalization in valence bond-hyperconjugation
No full textWe consider delocalization in small molecules. The valence bond technology allows an arbitrary division of the 1-electron space in strictly separate, but nonorthogonal, spaces. Allowing or obstructing orbital mixing between subspaces during the SCF procedure is associated with incorporating or eliminating the hyperconjugation effect. We show an example for tert-butyl and trimethylsilyl cations and radicals. For H2, for which really extensive basis sets are feasible, we extend the basis so far that the delocalization or hyperconjugation effect has nearly disappeare
Studying chemical vapor deposition processes with theoretical chemistry
Full text linkIn a chemical vapor deposition (CVD) process, a thin film of some material is deposited onto a surface via the chemical reactions of gaseous molecules that contain the atoms needed for the film material. These chemical reactions take place on the surface and in many cases also in the gas phase. To fully understand the chemistry in the process and thereby also have the best starting point for optimizing the process, theoretical chemical modeling is an invaluable tool for providing atomic-scale detail on surface and gas phase chemistry. This overview briefly introduces to the non-expert the main concepts, history and application of CVD, including the pulsed CVD variant known as atomic layer deposition, and put into perspective the use of theoretical chemistry in modeling these processes
Quimica-Teorica-IME/DPP_D_A_D_systems_Charge_Transfer: DPP_D_A_D_systems_Charge_Transfer
No full text<p>This release was made by the Theoretical Chemistry Group at the Military Institute of Engineering (Brazil).</p>
Development and Implementation of Methods in Theoretical Chemistry
No full textThe method development research in the field of theoretical chemistry is the never ending quest for methods that are faster, gives more accurate results, and expands the possibilities. The work in this thesis is no exception to that statement. Thus a CI routine more suited for calculations on large active spaces was implemented in the RASSCF code of Molcas; a new scheme for localizing multipole moments and polarizabilities were developed and implemented; and a parallel SCF code that provides super linear speed up saw the light of the day. These implementations were largely used throughout the remainder of the work, where the nuclear quadrupole moment of tin and the electronic spectrum of UO2 were determined; the photodissociation of bromoiodomethane was investigated; and the ability of localized properties to reproduce the electrostatic potential was tested
Development and Implementation of Methods in Theoretical Chemistry
No full textPopular Abstract in Swedish Att finna metoder som är snabbare, ger noggrannare resultat och utökar möjligheterna är det övergripande målet för forskningen inom teoretisk kemi. Denna avhandling utgör inget undantag. Sålunda, CI rutiner som möjliggör större beräkningar än tidigare har implementerats i RASSCF modulen i Molcas; nya metoder att lokalisera multipolmomement och polariserbarheter har utvecklats och programmerats; och ett parallellt SCF med superlinjär effektivitetsförbättring såg dagens ljus. Dessa implemetationer användes mestadeles i de avslutande undersökningarna, där kärnkvadrupolmomentet i tenn och det elektroniska spekrummet för UO2 bestämdes, fotodissociation av bromoiodometan undersöktes; och möjligheten provades att med lokaliserade egenskaper reproducera den elektrostatiska potentialen.The method development research in the field of theoretical chemistry is the never ending quest for methods that are faster, gives more accurate results, and expands the possibilities. The work in this thesis is no exception to that statement. Thus a CI routine more suited for calculations on large active spaces was implemented in the RASSCF code of Molcas; a new scheme for localizing multipole moments and polarizabilities were developed and implemented; and a parallel SCF code that provides super linear speed up saw the light of the day. These implementations were largely used throughout the remainder of the work, where the nuclear quadrupole moment of tin and the electronic spectrum of UO2 were determined; the photodissociation of bromoiodomethane was investigated; and the ability of localized properties to reproduce the electrostatic potential was tested
Theoretical Chemistry in Belgium - A Topical Collection from Theoretical Chemistry Accounts
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