Search results for "Orbit"
showing 10 items of 1104 documents
Dipolar coupling of nanoparticle-molecule assemblies: An efficient approach for studying strong coupling
2021
Strong light-matter interactions facilitate not only emerging applications in quantum and non-linear optics but also modifications of materials properties. In particular the latter possibility has spurred the development of advanced theoretical techniques that can accurately capture both quantum optical and quantum chemical degrees of freedom. These methods are, however, computationally very demanding, which limits their application range. Here, we demonstrate that the optical spectra of nanoparticle-molecule assemblies, including strong coupling effects, can be predicted with good accuracy using a subsystem approach, in which the response functions of the different units are coupled only a…
ChemInform Abstract: Spin Density Distribution in Transition Metal Complexes: Some Thoughts and Hints
2010
Abstract The spin density distribution in transition metal complexes is discussed in qualitative terms, taking into account the coexistence of spin delocalization and spin polarization mechanisms, with the help of numerical results for several complexes obtained from density functional calculations. The covalent character of the metal-ligand bonds as well as the σ- or π-characteristics of the partially filled d orbitals must be taken into account to qualitatively predict the sign of the spin density at a particular atom within a ligand. The same patterns can be applied to binuclear complexes and can be helpful in determining the ferro- or antiferromagnetic character of the exchange coupling…
Response calculations based on an independent particle system with the exact one-particle density matrix: Excitation energies
2012
Adiabatic response time-dependent density functional theory (TDDFT) suffers from the restriction to basically an occupied → virtual single excitation formulation. Adiabatic time-dependent density matrix functional theory allows to break away from this restriction. Problematic excitations for TDDFT, viz. bonding-antibonding, double, charge transfer, and higher excitations, are calculated along the bond-dissociation coordinate of the prototype molecules H2 and HeH+ using the recently developed adiabatic linear response phase-including (PI) natural orbital theory (PINO). The possibility to systematically increase the scope of the calculation from excitations out of (strongly) occupied into wea…
NMR chemical shift calculations within local correlation methods: the GIAO-LMP2 approach
2000
A scheme for the calculation of NMR chemical shifts using local second-order Moller–Plesset (LMP2) perturbation theory together with gauge-including atomic orbitals (GIAOs) is presented. Test calculations on the basis of a preliminary implementation within a conventional GIAO-MP2 code show that the deviations between GIAO-LMP2 and GIAO-MP2 are small, e.g., for 13C typically less than 1 ppm, and that the GIAO-LMP2 approach holds great promise for application to larger molecules.
Cholesky decomposition-based definition of atomic subsystems in electronic structure calculations
2010
Decomposing the Hartree-Fock one-electron density matrix and a virtual pseudodensity matrix, we obtain an orthogonal set of normalized molecular orbitals with local character to be used in post-Hartree-Fock calculations. The applicability of the procedure is illustrated by calculating CCSD(T) energies and CCSD molecular properties in reduced active spaces. © 2010 American Institute of Physics.
Perturbative treatment of triple excitations in coupled‐cluster calculations of nuclear magnetic shielding constants
1996
A theory for the calculation of nuclear magnetic shielding constants at the coupled‐cluster singles and doubles level augmented by a perturbative correction for connected triple excitations (CCSD(T)) has been developed and implemented. The approach, which is based on the gauge‐including atomic orbital (GIAO) ansatz, is illustrated by several numerical examples. These include a comparison of CCSD(T) and other highly correlated methods with full configuration interaction for the BH molecule, and a systematic comparison with experiment for HF, H2O,NH3, CH4, N2, CO, HCN, and F2. The results demonstrate the importance of triple excitations in establishing quantitative accuracy. Finally, the abil…
Fast noniterative orbital localization for large molecules
2006
We use Cholesky decomposition of the density matrix in atomic orbital basis to define a new set of occupied molecular orbital coefficients. Analysis of the resulting orbitals ("Cholesky molecular orbitals") demonstrates their localized character inherited from the sparsity of the density matrix. Comparison with the results of traditional iterative localization schemes shows minor differences with respect to a number of suitable measures of locality, particularly the scaling with system size of orbital pair domains used in local correlation methods. The Cholesky procedure for generating orthonormal localized orbitals is noniterative and may be made linear scaling. Although our present implem…
Time-dependent Landauer-Büttiker formula: Application to transient dynamics in graphene nanoribbons
2014
In this work we develop a time-dependent extension of the Landauer-B\"uttiker approach to study transient dynamics in time-dependent quantum transport through molecular junctions. A key feature of the approach is that it provides a closed integral expression for the time-dependence of the density matrix of the molecular junction after switch-on of a bias or gate potential which can be evaluated without the necessity of propagating individual single-particle orbitals. This allows for the study of time-dependent transport in large molecular systems coupled to wide band leads. As an application of the formalism we study the transient dynamics of zigzag and armchair graphene nanoribbons of diff…
Customised products for orbital wall reconstruction: a systematic review
2021
Abstract The purpose of this systematic review was to critically analyze the recent literature to present the state of the art in customized reconstruction of orbital fractures. Three electronic databases and manual search approaches were used to identify relevant articles. Only studies with a controlled clinical study design were included. Primary outcome was defined as the status of recovery (complete/partial functional and esthetic disturbances). The benefit of intra-surgical navigation should be described. Secondary outcome was defined as the time of surgery, post-surgical events and hospitalization. A total of eight studies out of 552 records identified met the inclusion criteria. Post…
Molecular and supramolecular structures of self-assembled Cu(II) and Co(II) complexes with 4,4’-[6-(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazine-2,4-…
2020
Abstract The molecular and supramolecular structures of [Cu(PTM)Cl2]∗0.75MeOH (1), [Co(PTM)Cl2]; (2A) and [Co(PTM)Cl2(EtOH)]; (2B) complexes, where PTM is 4,4’-[6-(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazine-2,4-diyl]dimorpholine, were presented. In complexes 1 and 2A, the Cu(II) and Co(II) are tetra-coordinated with a distorted tetrahedral coordination environment. In case of complex 2B, an additional ethanol molecule is found coordinated with Co(II) leading to a highly distorted penta-coordinated Co(II) complex. In all cases, the PTM ligand is acting as a bidentate NN-chelate. Hirshfeld surface analysis indicated the importance of H⋯H (49.0–55.1%), Cl⋯H (18.8–20.5%) and O⋯H (8.3–9.9%) co…