Effective Hamiltonian Model Research Articles

Modeling Charge Transport and Dynamics in Biomolecular Systems

Charge transport at the molecular scale builds the cornerstone of molecularelectronics (ME), a novel paradigm aiming at the realization of nanoscaleelectronics via tailored molecular functionalities. Biomolecular electronics,lying at the borderline between physics, chemistry and biology, can be con-sidered as a sub-field of ME. In particular, the potential applications of DNAoligomers either as template or as active device element in ME have stronglydrawn the attention of both experimentalist and theoreticians in the past years.While exploiting the self-assembling and self-recognition properties of DNAbased molecular systems is meanwhile a well-established field, the poten-tial of such biomolecules as active devices is much less clear mainly due tothe poorly understood charge conduction mechanisms. One key componentin any theoretical description of charge migration in biomolecular systems,and hence in DNA oligomers, is the inclusion of conformational fluctuationsand their coupling to the transport process. The treatment of such a problemaffords to consider dynamical effects in a non-perturbative way in contrastto, e.g., conventional bulk materials. Here we present an overview of recentwork aiming at combining molecular dynamic simulations and electronicstructure calculations with charge transport in coarse-grained effective model Hamiltonians. This hybrid methodology provides a common theoretical start-ing point to treat charge transfer/transport in strongly structurally fluctuatingmolecular-scale physical systems.

The CW-CRDS spectra of the 16O/18O isotopologues of ozone between 5930 and 6340 cm−1—Part 1: 16O16O18O

The first investigation of the very sensitive CW-Cavity Ring Down Spectra (noise equivalent absorption αmin≈1×10−10cm−1) of 18O enriched ozone isotopologues is reported. The ozone generation from 18O enriched oxygen molecules resulted in six isotopic species. The contributions of the 16O16O18O/16O18O16O and of the 18O18O16O/18O16O18O isotopomers were separated using two partial pressures of 16O2/18O2 mixtures. In the 5930–6340cm−1 range, the four dominant bands of 16O16O18O were vibrationally assigned as 2ν1+2ν2+3ν3_1, 2ν2+5ν3, 5ν1+ν3 and 2ν1+2ν2+3ν3_2. They correspond to the highest vibration excitations observed so far in an asymmetric CS ozone isotopologue. The rovibrational spectra for 18O enriched CS ozone species show specific features related to the nuclear spin statistics and to simultaneous symmetry allowed Coriolis and anharmonic accidental resonances, which are discussed. Altogether for the four new bands, 2155 rovibrational transitions were assigned up to Jmax=32. Observed line positions were fitted with rms deviations ranging from 0.005 to 0.01cm−1 using effective Hamiltonian models accounting for dark state perturbations. The derived band centers and rotational constants are in good agreement with new theoretical calculations from the molecular potential function. The corresponding line lists are provided as Supplementary Material.

Structural analysis and crystal-field calculations of Nd3+ in GdxLu1−xTaO4 (x = 0.85) polycrystalline

The crystal structural parameters of Nd3+-doped rare earth orthotantalate GdxLu1−xTaO4 (x = 0.85) are determined by applying the Rietveld refinement to its X-ray diffraction, and its emission and excitation spectra at 77 K are analysed. The relativistic model of ab initio self-consistent DV-Xα method, which is applied to the cluster NdO8 in GdxLu1−xTaO4, and the effective Hamiltonian model are used to investigate its spin—orbit and crystal-field parameters. The free-ions and crystal-field parameters are fitted to the experimental energy levels at 77 K with a root-mean-square deviation of 14.92 cm−1. According to the crystal-field calculations, 96 levels of Nd3+ are assigned. Finally, the fitting results of free-ions and crystal-field parameters are compared with those already reported for Nd3+:YAlO3. The results indicate that the free-ion parameters are similar to those of the Nd3+ in GdxLu1−xTaO4 and YAlO3 hosts, and the crystal-field interaction of Nd3+ in GdxLu1−xTaO4 is stronger than that in YAlO3.

Impact of the valley degree of freedom on the control of donor electrons near a Si/SiO2interface

We analyze the valley composition of one electron bound to a shallow donor close to a Si/barrier interface as a function of an applied electric field. A full six-valley effective mass model Hamiltonian is adopted. For low fields, the electron ground state is essentially confined at the donor. At high fields the ground state is such that the electron is drawn to the interface, leaving the donor practically ionized. Valley splitting at the interface occurs due to the valley-orbit coupling, ${V}_{\mathrm{vo}}^{I}=|{V}_{\mathrm{vo}}^{I}|{e}^{i\ensuremath{\theta}}$. At intermediate electric fields, close to a characteristic shuttling field, the electron states may constitute hybridized states with valley compositions differing from the donor and the interface ground states. The full spectrum of energy levels shows crossings and anticrossings as the field varies. The degree of level repulsion, thus, the width of the anticrossing gap, depends on the relative valley compositions, which vary with $|{V}_{\mathrm{vo}}^{I}|$, $\ensuremath{\theta}$ and the interface-donor distance. We focus on the valley configurations of the states involved in the donor-interface tunneling process, given by the anticrossing of the three lowest eigenstates. A sequence of two anticrossings takes place and the complex phase $\ensuremath{\theta}$ affects the symmetries of the eigenstates and level anticrossing gaps. We discuss the implications of our results on the practical manipulation of donor electrons in Si nanostructures.

Origin of Ferroelectricity in High-TcMagnetic Ferroelectric CuO

Cupric oxide is a unique magnetic ferroelectric material with a transition temperature significantly higher than the boiling point of liquid nitrogen. However, the mechanism of high-T(c) multiferroicity in CuO remains puzzling. In this Letter, we clarify the mechanism of high-T(c) multiferroicity in CuO by using combined first-principles calculations and an effective hamiltonian model. We find that CuO contains two magnetic sublattices, with strong intrasublattice interactions and weakly frustrated intersublattice interactions. The weak spin frustration leads to incommensurate spin excitations that dramatically enhance the entropy of the multiferroic phase and eventually stabilize that phase in CuO.

Analysis of the CRDS spectrum of 18O3 between 6950 and 7125 cm−1

The absorption spectrum of the 18O3 isotopologue of ozone was recorded by CW-Cavity Ring Down Spectroscopy in the 6950–7125cm−1 region. The typical noise equivalent absorption of the recordings is αmin ≈1×10−10cm−1. The spectrum is dominated by three very weak bands: 3ν1+5ν3 near 7009cm−1 and the ν2+7ν3 and 4ν2+5ν3 interacting bands near 7100cm−1. In total 260, 206 and 133 transitions were assigned for the 3ν1+5ν3, ν2+7ν3 and 4ν2+5ν3 bands, respectively. The line positions of the 3ν1+5ν3 band were modelled using an effective Hamiltonian (EH) model involving two dark states – (601) and (252) – in interaction with the (305) bright state. The EH model developed for the ν2+7ν3 and 4ν2+5ν3 bands involves only the (017) and (045) interacting bright states. Line positions could be reproduced with rms deviations on the order of 0.01cm−1 and the dipole transition moment parameters were determined for the three observed bands. The obtained set of parameters and the experimentally determined energy levels were used to generate a list of 984 transitions of the three bands which is provided as Supplementary Material.

High sensitivity CW-Cavity Ring Down Spectroscopy of N2O between 6950 and 7653 cm−1 (1.44–1.31 μm): I. Line positions

The absorption spectrum of nitrous oxide, N2O, has been recorded by CW-Cavity Ring Down Spectroscopy between 6950 and 7653cm−1. The spectra were obtained at Doppler limited resolution using a CW-CRDS spectrometer based on a series of fibered DFB laser diodes. The typical noise equivalent absorption, in the order of αmin≈1×10−10cm−1, allowed for the detection of lines with intensity as small as 1×10–29cm/molecule.The positions of 7203 lines of four isotopologues (14N216O, 14N15N16O, 15N14N16O and 14N218O) were measured with a typical accuracy of 1.0×10−3cm−1. The transitions were rovibrationally assigned on the basis of the global effective Hamiltonian models developed for each isotopologue. The band by band analysis allowed for the determination of the rovibrational parameters of more than 95 bands, most of them being newly reported while new rotational transitions are measured for the others. The measured line positions of the main isotopologue are found to be in good agreement with the predictions of the effective Hamiltonian model but a few deviations up to 0.20cm−1 are observed. Local rovibrational perturbations were evidenced for several bands. The interaction mechanisms and the perturbers were univocally assigned on the basis of the effective Hamiltonian models.

Geometrical Aspects of Drying in a Capped Capillary: a DFT Study

The order of the liquid–solid phase transition of a fluid confined by a capillary of two parallel walls can be changed from first to second order if the capillary is capped at one end by a third wall. This change of order of the phase transition was predicted using an effective interfacial Hamiltonian model and was recently confirmed by a microscopic density functional theory study. In this study some geometrical aspects of the continous transition in a capped capillary are considered within the framework of density functional theory.

Global modeling of the 14N216O line positions within the framework of the polyad model of effective Hamiltonian

The global modeling of 14N216O line positions in the 0–9700cm−1 region has been performed using the polyad model of effective Hamiltonian. The effective Hamiltonian parameters were fitted to the line positions collected from an exhaustive review of the literature. A number of lines perturbed by interpolyad resonance interactions were excluded from the fit. The dimensionless weighted standard deviation of the fit is 4.06. The fitted set of 138 effective Hamiltonian parameters allowed reproducing 37,353 measured line positions of 325 bands with an RMS value of 0.00423cm−1.

High-resolution Infrared Spectroscopy of 15N216O in 1650–3450 cm−1

High-resolution ro-vibrational spectroscopy of 15N216O in 1650–3450 cm−1 region is studied using highly enriched isotopologue sample. The positions of more than 7300 lines of 15N216O isotopologue were measured with a typical accuracy of 5.0×10−4 cm−1. The transitions were rovibrationally assigned on the basis of the global effective Hamiltonian model. The band by band analysis allowed for the determination of the rovibrational parameters of a total of 73 bands. 29 of them are newly reported and more rotational transitions have been observed for the others. The maximum deviation of the preidictions of the effective Hamiltonian model is up to 0.70 cm−1 for the 15N216O species.

High sensitivity CW-Cavity Ring Down Spectroscopy of N 2O near 1.28 μm

The absorption spectrum of nitrous oxide, N 2O, in normal isotopic abundance has been recorded by CW-Cavity Ring Down Spectroscopy between 7647 and 7918 cm −1. The spectra were obtained at Doppler limited resolution by using a CW-CRDS spectrometer based on a series of fibered DFB lasers. The typical noise equivalent absorption on the order of α min ≈ 1 × 10 −10 cm −1, allowed for the detection of lines with intensity as weak as 2 × 10 −29 cm/molecule. The positions of 2272 lines of five isotopologues ( 14N 2 16O, 15N 14N 16O, 14N 15N 16O, 14N 2 18O and 14N 2 17O), were measured with a typical accuracy of 1.0 × 10 −3 cm −1. The transitions were rovibrationally assigned on the basis of the global effective Hamiltonian models respective to each isotopologue. The band by band analysis allowed for the determination of the rovibrational parameters of a total of 30 bands, 19 of them being newly reported while new rotational transitions are measured for the others. The maximum deviation of the predictions of the effective Hamiltonian models is 0.18 cm −1 for the line positions of the main isotopologue and up to 1.3 cm −1 for the 14N 2 18O species. Local rovibrational perturbations were evidenced for three bands of 14N 2 16O and the ν 1 + 3 ν 3 band of 14N 2 17O. The interaction mechanisms and the perturbers were univocally assigned on the basis of the effective Hamiltonian models.

QCD inspired relativistic effective Hamiltonian model for mesons

A QCD inspired relativistic effective Hamiltonian model for mesons has been proposed based on light-front QCD effective Hamiltonian. The squared invariant rest mass operator is used as the effective Hamiltonian. The model has been improved significantly in four major aspects: i) it is proved that in constituent rest frame and in internal Hilbert subspace, the total angular momentum of mesons is conserved, the mass eigen equation can be expressed in total angular momentum representation and in terms of a set of coupled radial eigen equations; ii) a relativistic confining potential is introduced to describe the excited states; iii) an SU(3) flavor mixing interaction is included and a set of coupled mass eigen equations are obtained for different flavor components; iv) the L–S coupling and the tensor interaction are taken into full account. The model has been applied to describe the whole meson spectra of about 265 mesons with available data. The meson masses, squared radii, and decay constants are calculated, and the agreement with data is satisfying. For the mesons whose mass data have large experimental uncertainty, the model produces certain mass values for test. For some mesons whose total angular momenta and parities are not assigned experimentally, the model gives a prediction of their spectroscopic configuration LJ2S+1. The radial excitation spectra are also analyzed, the discrepancy between the calculated spectra and the data indicates angular momentum effect and higher Fock space effect for some mesons. The relation between our model and the infrared conformal scaling invariance as well as the holographic light front QCD meson model is discussed.

Time-averaged quantum dynamics and the validity of the effective Hamiltonian model

We develop a technique for finding the dynamical evolution in time of an averaged density matrix. The result is an equation of evolution that includes an Effective Hamiltonian, as well as decoherence terms in Lindblad form. Applying the general equation to harmonic Hamiltonians, we confirm a previous formula for the Effective Hamiltonian together with a new decoherence term which should in general be included, and whose vanishing provides the criteria for validity of the Effective Hamiltonian approach. Finally, we apply the theory to examples of the AC Stark Shift and Three- Level Raman Transitions, recovering a new decoherence effect in the latter.

Statistics of resonance states in a weakly open chaotic cavity with continuously distributed losses

In this Rapid Communication, we demonstrate that a non-Hermitian random matrix description can account for both spectral and spatial statistics of resonance states in a weakly open chaotic wave system with continuously distributed losses. More specifically, the statistics of resonance states in an open two-dimensional chaotic microwave cavity are investigated by solving the Maxwell equations with lossy boundaries subject to Ohmic dissipation. We successfully compare the statistics of its complex-valued resonance states and associated widths with analytical predictions based on a non-Hermitian effective Hamiltonian model defined by a finite number of fictitious open channels.

Charge migration through DNA molecules in the presence of mismatches

Charge transport characteristics of short double-strand DNA including mismatches are studied within a methodology combining molecular-dynamics (MD) simulations and electronic-structure calculations based on a fragment orbital approach. Electronic parameters and transmission probabilities are computed along the MD trajectory. We find that in the course of the MD simulation the energetic position of frontier orbitals may be interchanged. As a result, the highest-occupied molecular orbital can temporarily have a large weight on the backbones as a function of time. This shows that care must be taken when projecting the electronic structure onto effective low-dimensional model Hamiltonians to calculate transport properties. Further, the transport calculations indicate a suppression of the charge migration efficiency when introducing a single GT or AC mismatch in the DNA sequence.

Effective Hamiltonian approach to the non-Markovian dynamics in a spin bath

We investigate the dynamics of a central spin that is coupled to a bath of spins through a non-uniform distribution of coupling constants. Simple analytical arguments based on master equation techniques as well as numerical simulations of the full von Neumann equation of the total system show that the short-time damping and decoherence behaviour of the central spin can be modelled accurately through an effective Hamiltonian involving a single effective coupling constant. The reduced short-time dynamics of the central spin is thus reproduced by an analytically solvable effective Hamiltonian model.

First assignment of the 5 ν4 and ν2+4 ν4 band systems of 12CH 4 in the 6287–6550 cm −1 region

This paper reports the first assignment of rovibrational transitions of the 5 ν 4 and ν 2+4 ν 4 band systems of 12CH 4 in the 6287–6550 cm −1 region, which is usually referred to as part of the 1.58 μm methane transparency window. The analysis was based on two line lists previously obtained in Grenoble by cavity ring down spectroscopy at T=297 and 79 K completed by three long-path Fourier transform spectra recorded in Reims (at 290 K, L=1603 m, P=1–34 mbar). In order to determine the dipole transition moment parameters and quantify the intensity borrowing due to the resonance interactions, we had to include in the fit of the effective Hamiltonian model some lines of the stronger ν 1+3 ν 4 and ν 2+4 ν 4 bands. For this purpose, intensities of 179 additional lines were retrieved from FTS spectra above 6550 cm −1 though the analysis of these higher bands is not complete. About 1955 experimental line positions and 1462 line intensities were fitted with RMS standard deviations of 0.003 cm −1 and 13.1%, respectively. A line list of 8029 calculated and observed transitions which are considered as dominant was constructed for 12CH 4 in the 6287–6550 cm −1 region. This is the first high-resolution analysis and modelling of 5-quanta band systems of 12CH 4.

Structural stability versus conformational sampling in biomolecular systems: Why is the charge transfer efficiency in G4-DNA better than in double-stranded DNA?

The electrical conduction properties of G4-DNA are investigated using a hybrid approach, which combines electronic structure calculations, molecular dynamics (MD) simulations, and the formulation of an effective tight-binding model Hamiltonian. Charge transport is studied by computing transmission functions along the MD trajectories. Though G4-DNA is structurally more stable than double-stranded DNA (dsDNA), our results strongly suggest that the potential improvement of the electrical transport properties in the former is not necessarily related to an increased stability, but rather to the fact that G4 is able to explore in its conformational space a larger number of charge-transfer active conformations. This in turn is a result of the non-negligible interstrand matrix elements, which allow for additional charge transport pathways. The higher structural stability of G4 can however play an important role once the molecules are contacted by electrodes. In this case, G4 may experience weaker structural distortions than dsDNA and thus preserve to a higher degree its conduction properties.

Light Flavor Vector and Pseudo Vector Mesons from a Light-Cone QCD Inspired Effective Hamiltonian Model with SU(3) Flavor Mixing Interactions

Based on the light-cone effective Hamiltonian with confining potential and SU(3) flavor mixing interactions, the flavor mixing mesons on the u, d, and s quark sectors are investigated. The mass eigen equations of the flavor mixing vector and pseudo vector mesons are solved. The calculated masses are in good agreement with the experimental data.

Models of organometallic complexes for optoelectronic applications

Organometallic complexes have potential applications as the optically active components of organic light emitting diodes (OLEDs) and organic photovoltaics (OPV). Development of more effective complexes may be aided by understanding their excited state properties. Here we discuss two key theoretical approaches to investigate these complexes: first principles atomistic models and effective Hamiltonian models. We review applications of these methods, such as, determining the nature of the emitting state, predicting the fraction of injected charges that form triplet excitations, and explaining the sensitivity of device performance to small changes in the molecular structure of the organometallic complexes.