Search results for "basis"

showing 10 items of 760 documents

Explicitly Correlated Electrons in Molecules

2011

Basis set superposition errorQuantum chemistry composite methodsChemistryQuantum mechanicsQuantum Monte CarloPotential energy surfaceMoleculeGeneral ChemistryElectronSTO-nG basis setsChemical Reviews
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Verso una dimensione narrativa delle mappe

2021

Tra il pensiero e la costruzione dell’architettura il disegno ha un ruolo baricentrico per connettere i diversi protagonisti di una realizzazione e per coinvolgere la collettività facendo percepire inedite prospettive. La scrittura si rivela utile per esplicitare ciò che nella grafica è sotteso e per stabilire un ordine nuovo nel ragionamento progettuale. I rapporti fra segni e significati si moltiplicano nei sistemi informativi recenti in cui si ha la sensazione di poter dire moltissimo (dati numerici e spaziali) ma a volte sfugge quella sintesi indispensabile per una interpretazione concreta, finalizzata alla costruzione di possibili esperienze fisiche. Per l’esplorazione dell’uso di dive…

Between the idea and the construction of the architecture the drawing plays a central role to connect the different protagonists of a project. It involves the community by envisaging unprecedented perspectives. Writing is useful to explicit the graphics and establish a new order in the design reasoning. The relationships between signs and meanings multiply in recent information systems in which it seems possible to conclude a lot (thanks to numerical and spatial data) but sometimes a synthesis is missing though that synthesis is fundamental to create new physical experiences. For the exploration of the use of different architectural languages and for the push towards the project rather than a sterile cataloging the case of the Piano Programma for the historic center of Palermo (Giuseppe Samonà Giancarlo De Carlo Umberto Di Cristina Anna Maria Sciarra Borzí 1979-82) reveals to be ambitious. Giuseppe Samonà integrates the classical representation based on Monge's projections with photographs and iconic drawings associating signs with a linguistic-structural communication capable of expressing the relationships between the parts at the basis of a morphological approach to the plan. The graphic story ("second language") of the urban fabric has creative implications expressed by images and annotations ("first language") useful for decoding them. Since the plan focuses on the potential of a storytelling that orients the imagination of its readers (designers citizens politicians) it can contribute to the study titled "B4R– BRANDING 4 RESILIENCE - Tourist infrastructure as a tool to enhance small villages by drawing resilient communities and new open habitats” as a starting point for the mapping in which GIS analysis and multidisciplinary data (geometric topological and quantitative) relating to some villages of the internal Sicily shall translate into a new architectural urban and landscape quality.Settore ICAR/14 - Composizione Architettonica E Urbana
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A theoretical study of the electronic spectrum of biphenyl

1995

Abstract The electronic spectrum of biphenyl in the energy range up to 6.0 eV has been studied using multiconfigurational second-order perturbation theory (CASPT2) and a basis set of ANO type, including polarization functions on all carbon atoms. The calculated spectrum gives conclusive assignments to all valence excited singlet states and the low-lying triplet states. The change of the torsional angle between the two benzene rings in the different excited states is shown to be of considerable importance and explains the different excitation energies observed in the gas phase as compared to solution or crystalline biphenyl at low temperatures. The intense transition to the 1 1B1u state is m…

BiphenylValence (chemistry)General Physics and AstronomyPolarization (waves)symbols.namesakechemistry.chemical_compoundchemistryExcited stateRydberg formulasymbolsPhysical and Theoretical ChemistryAtomic physicsBenzeneExcitationBasis setChemical Physics Letters
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CCSDT calculations of molecular equilibrium geometries

1997

Abstract CCSDT equilibrium geometries of CO, CH2, F2, HF, H2O and N2 have been calculated using the correlation-consistent cc-pVXZ basis sets. Similar calculations have been performed for SCF, CCSD and CCSD(T). In general, bond lengths decrease when improving the basis set and increase when improving the N-electron treatment. CCSD(T) provides an excellent approximation to CCSDT for bond lengths as the largest difference between CCSDT and CCSD(T) is 0.06 pm. At the CCSDT/cc-pVQZ level, basis set deficiencies, neglect of higher-order excitations, and incomplete treatment of core-correlation all give rise to errors of a few tenths of a pm, but to a large extent, these errors cancel. The CCSDT/…

Bond lengthBasis (linear algebra)Computational chemistryChemistryGeneral Physics and AstronomyPhysical and Theoretical ChemistryMolecular physicsBasis setChemical Physics Letters
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On the geometry of the HO3 radical

2008

Abstract We discuss the equilibrium structure of the hydrogen trioxy radical (HO3). The CCSD(T) geometry at the approximate basis set limit, in conjunction with the geometry obtained using the CCSDT method and a moderate basis set, suggests an equilibrium HO–OO bond length of approximately 1.59 A.

Bond lengthHydrogenchemistryStructure (category theory)General Physics and Astronomychemistry.chemical_elementMoleculeGeometryLimit (mathematics)Physical and Theoretical ChemistryBasis setChemical Physics
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A theoretical determination of the dissociation energy of the nitric oxide dimer

1994

Multi-reference CI methods have been applied to determine the dissociation energy and structure of thecis-N2O2 molecule. The convergence of the theoretical result has been checked with respect to a systematic expansion of the one-electron basis set and the multi-reference CI wave function. The best calculated value, 13.8 kJ/mol, is in agreement with the experimental value, 12.2 kJ/mol. It has been obtained with an extended ANO-type basis set [6s5p3d2f], including the effect of the basis set superposition error (BSSE) in the geometry optimization, and additional effects, such as the electron correlation of core electrons and relativistic corrections, using the average coupled pair functional…

Bond lengthPhysicsMolecular geometryElectronic correlationCore electronAb initio quantum chemistry methodsThermodynamicsChiropracticsPhysical and Theoretical ChemistryConfiguration interactionBond-dissociation energyBasis setTheoretica Chimica Acta
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Design of neutral Lewis superacids of group 13 elements.

2011

A general approach toward superstrong neutral Lewis acids, featuring both the pyramidalization of acceptor molecules and the introduction of electron-withdrawing substituents, is proposed and examined theoretically. Complexes of group 13 element derivatives with ammonia at the B3LYP and MP2 levels of theory with def2-TZVPP basis set are considered as examples. Pyramidalization of the acceptor molecule significantly increases its Lewis acidity (by 50-60 kJ mol(-1) for aluminum and gallium compounds and by 120-130 kJ mol(-1) for boron compounds). An additional increase of the complex stability of 55-75 kJ mol(-1) may be achieved by fluorination. The combined increase of the bond dissociation …

Boron groupchemistry.chemical_elementAcceptorBond-dissociation energyInorganic ChemistrychemistryComputational chemistryOrganic chemistryMoleculeLewis acids and basesPhysical and Theoretical ChemistryGalliumBoronBasis setInorganic chemistry
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A first-principles DFT study of UN bulk and (001) surface: comparative LCAO and PW calculations.

2008

LCAO and PW DFT calculations of the lattice constant, bulk modulus, cohesive energy, charge distribu- tion, band structure, and DOS for UN single crystal are analyzed. It is demonstrated that a choice of the uranium atom relativistic effective core potentials considerably affects the band structure and magnetic structure at low tem- peratures. All calculations indicate mixed metallic-covalent chemical bonding in UN crystal with U5f states near the Fermi level. On the basis of the experience accumulated in UN bulk simulations, we compare the atomic and elec- tronic structure as well as the formation energy for UN(001) surface calculated on slabs of different thickness using both DFT approach…

Bulk modulusChemistryFermi levelGeneral ChemistryMolecular physicsComputational Mathematicssymbols.namesakeCrystallographyDelocalized electronAtomic orbitalLinear combination of atomic orbitalsAtomsymbolsElectronic band structureBasis setJournal of computational chemistry
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A Geometric Algorithm for Ray/Bézier Surfaces Intersection Using Quasi-Interpolating Control Net

2008

In this paper, we present a new geometric algorithm to compute the intersection between a ray and a rectangular Bezier patch. The novelty of our approach resides in the use of bounds of the difference between a Bezier patch and its quasi-interpolating control net. The quasi-interpolating polygon of a Bezier surface of arbitrary degree approximates the limit surface within a precision that is function of the second order difference of the control points, which allows for very simple projections and 2D intersection tests to determine sub-patches containing a potential intersection. Our algorithm is simple, because it only determines a 2D parametric interval containing the solution, and effici…

Bézier surfaceStatistical classificationSpline (mathematics)Computer Science::GraphicsComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISIONBasis functionAlgorithm designBézier curveAlgorithmComputingMethodologies_COMPUTERGRAPHICSInterpolationMathematicsParametric statistics2008 IEEE International Conference on Signal Image Technology and Internet Based Systems
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Experimental and DFT studies on competitive heterocyclic rearrangements. part 2: A one-atom side-chain versus the classic three-atom side-chain (Boul…

2007

The experimental investigation of the base-catalyzed rearrangements of 3-acylamino-1,2,4-oxadiazoles evidenced a new reaction pathway which competes with the well-known ring-degenerate Boulton- Katritzky rearrangement (BKR). The new reaction consists of a one-atom side-chain rearrangement that is base-activated, occurs at a higher temperature than the BKR, and irreversibly leads to the corresponding 2-acylamino-1,3,4-oxadiazoles. An extensive DFT study is reported to elucidate the proposed reaction mechanism and to compare the three possible inherent routes: (i) the reversible three-atom side-chain ring-degenerate BKR, (ii) the ring contraction-ring expansion route (RCRE), and (iii) the one…

CASCADE REARRANGEMENTPHOTOCHEMICAL APPROACHDEGENERATE EQUILIBRATION124-OXADIAZOLE SERIESMONOCYCLIC REARRANGEMENT5-MEMBERED HETEROCYCLESEXPEDIENT ROUTEPHOTOINDUCED MOLECULAR-REARRANGEMENTSGENERALIZED SYNTHESISBASIS-SETS
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