Search results for " Density Functional Theory."
showing 10 items of 106 documents
Dynamic Self-Consistent Field Approach for Studying Kinetic Processes in Multiblock Copolymer Melts
2020
The self-consistent field theory is a popular and highly successful theoretical framework for studying equilibrium (co)polymer systems at the mesoscopic level. Dynamic density functionals allow one to use this framework for studying dynamical processes in the diffusive, non-inertial regime. The central quantity in these approaches is the mobility function, which describes the effect of chain connectivity on the nonlocal response of monomers to thermodynamic driving fields. In a recent study [Mantha et al, Macromolecules 53, 3409 (2020)], we have developed a method to systematically construct mobility functions from reference fine-grained simulations. Here we focus on melts of linear chains …
Vibrational spectra and DFT calculations of PPV-oligomers
2003
The first two members of the p-phenylenevinylene- oligomer family (i. e. 1, 4-distyrylbenzene [DSB] and 4, 4'-distyrylstilbene [DSS]) were synthesized and their infrared and Raman spectra recorded and empirically assigned. Molecular geometries were optimized for the planar point group (C2h) by the density functional theory (DFT) method using the B3LYP functional and 6-31G* basis set. Calculations of vibrational spectra, including intensities, were carried out subsequently using the DFT method with the same basis set and linear scaling was applied. Calculated vibrational wavenumbers are in a fair agreement with our own experimental spectra. In order to explore changes in vibrational dynamics…
Radical cations and dications of bis[1]benzothieno[1,4]thiazine isomers
2021
Bis[1]benzothieno[1,4]thiazines (BBTT) are particularly electron-rich S,N-heteropentacenes and their radical cations and dications can be relevant intermediates in charge transport materials. All three regioisomers of N-p-fluorophenyl-BBTT (syn–syn, syn–anti, and anti–anti) were studied. A reliable preparation of radical cations and dications using antimony pentachloride as an oxidant gives deeply colored salts. The electronic structure of the radical cations was assessed by EPR spectroscopy, whereas dicationic structures were characterized by NMR spectroscopy. In addition, a deeper insight into the electronic structure was experimentally and computationally obtained by UV/Vis spectroscopy …
Assignment of Configuration in a Series of Dioxolanone-Type Secondary Metabolites fromGuignardia bidwellii- A Comparison of VCD and ECD Spectroscopy
2013
The absolute configurations of a series of phytotoxic dioxolanone-type secondary metabolites isolated from culture filtrates of the grape black rot fungus Guignardia bidwellii were determined by vibrational circular dichroism (VCD) spectroscopy in the mid-IR frequency range. Comparison of the recorded data with DFT calculations showed good agreement between experiment and theory for VCD, whereas electronic circular dichroism (ECD) data for the compounds matched poorly with the predicted spectra obtained by time-dependent DFT (TDDFT) calculations at the same level of theory.
Combined spectroscopic and theoretical analysis of the binding of a water-soluble perylene diimide to DNA/RNA polynucleotides and G-quadruplexes.
2021
We present here a combined spectroscopic and theoretical analysis of the binding of N,N’-bis(2-(1-piperazino)ethyl)-3,4,9,10-perylenetetracarboxylic acid diimide dichloride (PZPERY) to different biosubstrates. Absorbance titrations and circular dichroism experiments, melting studies and isothermal calorimetry (ITC) titrations reveal a picture where the binding to natural double-stranded DNA is very different from that to double and triple-stranded RNAs (poly(A)∙poly(U) and poly(U)∙poly(A)⁎poly(U)). As confirmed also by the structural and energetic details clarified by density functional theory (DFT) calculations, intercalation occurs for DNA, with a process driven by the combination of aggr…
New Austalides from the Sponge-Associated Fungus Aspergillus sp.
2011
Chromatographic separation of a crude extract obtained from the fungus Aspergillus sp., isolated from the Mediterranean sponge Tethya aurantium, yielded five new meroterpenoid metabolites, austalides M–Q (1–5), together with nine known compounds (6–13). The structures of the new compounds were unambiguously elucidated on the basis of extensive 1D and 2D NMR methods and by mass spectral analysis. Furthermore, the absolute configurations of 1 and 4 were determined by time-dependent density functional theory electronic circular dichroism (TDDFT ECD) calculations, allowing the assignment of the absolute configuration of analogous compounds 2, 3, and 5. The calculations revealed that the conform…
Existence, uniqueness, and construction of the density-potential mapping in time-dependent density-functional theory
2014
In this work we review the mapping from densities to potentials in quantum mechanics, which is the basic building block of time-dependent density-functional theory and the Kohn-Sham construction. We first present detailed conditions such that a mapping from potentials to densities is defined by solving the time-dependent Schr\"odinger equation. We specifically discuss intricacies connected with the unboundedness of the Hamiltonian and derive the local-force equation. This equation is then used to set up an iterative sequence that determines a potential that generates a specified density via time propagation of an initial state. This fixed-point procedure needs the invertibility of a certain…
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…
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…
Oscillator Strengths of Electronic Excitations with Response Theory using Phase Including Natural Orbital Functionals
2013
The key characteristics of electronic excitations of many-electron systems, the excitation energies ωα and the oscillator strengths fα, can be obtained from linear response theory. In one-electron models and within the adiabatic approximation, the zeros of the inverse response matrix, which occur at the excitation energies, can be obtained from a simple diagonalization. Particular cases are the eigenvalue equations of time-dependent density functional theory (TDDFT), time-dependent density matrix functional theory, and the recently developed phase-including natural orbital (PINO) functional theory. In this paper, an expression for the oscillator strengths fα of the electronic excitations is…