scholarly journals Gerade-ungerade symmetry breaking in HD: States close to N=2 dissociation limit

2008 ◽  
Vol 6 (1) ◽  
pp. 29-40
Author(s):  
Tasko Grozdanov
Keyword(s):  
Experimental Data ◽  
Molecular Dynamics ◽  
Symmetry Breaking ◽  
Excellent Agreement ◽  
Bound States ◽  
Electronic States ◽  
Dissociation Limit ◽  
Empirical Potential ◽  
Oppenheimer Approximation ◽  
Semi Empirical

We review the consequences of the gerade-ungerade symmetry breaking in HD molecule. A particular attention is devoted to electronic states close to n=2 dissociation limit. The effects of the breakdown of the Born-Oppenheimer approximation are discussed. For the description of the molecular dynamics the formulation of the coupled-sates method is given. The method is applied to calculations of loosely bound states in the outer well of the II'1?g potential. The results are in excellent agreement with experimental data and calculations based on a semi-empirical potential.

scholarly journals Gerade/ungerade symmetry-breaking in HD at the n = 2 dissociation limit

2000 ◽  
Vol 78 (5-6) ◽  
pp. 567-578 ◽  
Author(s):  
A de Lange ◽  
E Reinhold ◽  
W Hogervorst ◽  
W Ubachs
Keyword(s):  
Binding Energy ◽  
Symmetry Breaking ◽  
Extreme Ultraviolet ◽  
Dissociation Limit ◽  
Pulsed Lasers ◽  
Excitation Scheme ◽  
Empirical Potential ◽  
Vibrational Levels ◽  
Infrared Excitation ◽  
Semi Empirical

We report on a study of the I'1Πg outer well state of HD. Via a resonance-enhanced XUV + IR (extreme ultraviolet + infrared) excitation scheme, rovibronic levels (v = 0-2, J = 1-4) are populated and probed by pulsed lasers. Level energies are measured with an accuracy of [Formula: see text] 0.03 cm-1. Due to gerade-ungerade symmetry breaking, the long-range behavior of the I' potential in HD deviates from that of H2 and D2. When this deviation is taken into account a semi-empirical potential for the I'1Πg state may be constructed, resulting in better agreement with the observed level energies than derived from an adiabatic ab initio potential. With this new potential it is predicted that the I' well can sustain only 4 vibrational levels, with the v = 3 level having a binding energy of [Formula: see text]1.38(3) cm-1. PACS Nos.: 33.80.Rv, 34.20.Cf, 33.20.Ni, 31.50.+w

scholarly journals An Investigation into the Approximations Used in Wave Packet Molecular Dynamics for the Study of Warm Dense Matter

Plasma ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 294-308
Author(s):  
William A. Angermeier ◽  
Thomas G. White
Keyword(s):  
Molecular Dynamics ◽  
Wave Packet ◽  
Hydrogen Plasma ◽  
Valence Bond ◽  
Dense Matter ◽  
Basis Set ◽  
Warm Dense Matter ◽  
Scaling Parameters ◽  
Oppenheimer Approximation ◽  
Semi Empirical

Wave packet molecular dynamics (WPMD) has recently received a lot of attention as a computationally fast tool with which to study dynamical processes in warm dense matter beyond the Born–Oppenheimer approximation. These techniques, typically, employ many approximations to achieve computational efficiency while implementing semi-empirical scaling parameters to retain accuracy. We investigated three of the main approximations ubiquitous to WPMD: a restricted basis set, approximations to exchange, and the lack of correlation. We examined each of these approximations in regard to atomic and molecular hydrogen in addition to a dense hydrogen plasma. We found that the biggest improvement to WPMD comes from combining a two-Gaussian basis with a semi-empirical correction based on the valence-bond wave function. A single parameter scales this correction to match experimental pressures of dense hydrogen. Ultimately, we found that semi-empirical scaling parameters are necessary to correct for the main approximations in WPMD. However, reducing the scaling parameters for more ab-initio terms gives more accurate results and displays the underlying physics more readily.

Анализ вычислительных и экспериментальных исследований переключения поляризации в ПВДФ и П (ВДФ-ТрФЭ) сегнетоэлектрических пленках на наноуровне

2015 ◽  
Vol 10 (2) ◽  
pp. 372-386 ◽  
Author(s):  
В.С. Быстров ◽  
V.S. Bystrov
Keyword(s):  
Experimental Data ◽  
Molecular Dynamics ◽  
Electric Field ◽  
Quantum Chemical ◽  
Polyvinylidene Fluoride ◽  
Domain Switching ◽  
Polarization Switching ◽  
Molecular Structures ◽  
Switching Mechanism ◽  
Semi Empirical

In this paper, molecular models are used to investigate and analyze the polarization switching in the polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) Langmuir-Blodgett (LB) nanofilms, in comparison with the experimental data at the nanoscale. Quantum-mechanical calculations and modeling, as well as molecular dynamics (MD) simulations based on semi-empirical quantum-chemical methods (such as PM3), show that the energy of the studied PVDF and P (VDF-TrFE) molecular structures, and their polarization switching proceed by the intrinsic homogeneous switching mechanism in the framework of the phenomenological theory of Landau-Ginzburg-Devonshire (LGD) in the linear approximation at low values of the electric field. The magnitude of the resulting critical coercive field is within the EC ~ 0.5 ... 2.5 GV/m, which is consistent with experimental data. It is also found that the uniform polarization switching mechanism of the polymer chains PVDF and P (VDF-TrFE) is due to the quantum properties of the molecular orbitals of the electron subsystem. This is clearly seen in both the polarization hysteresis loops, and the total energy changes. In this case, the turnover chain time, obtained by molecular dynamics within semi-empirical quantum-chemical PM3 approach in a limited Hartree-Fock approximation, when approaching this critical point, increases sharply, tending to infinity, which corresponds to the theory of LGD. Otherwise, at the high values of the applied electric field the polarization switching correspond to the extrinsic domain mechanism in the frame of the microscopic Kolmogorov–Avrami–Ishibashi (KAI) theory, describing bulk ferroelectric crystals and thick films. The performed analysis of computational and experimental data allows us to estimate the critical sizes of the possible transition region approximately on the order of 10 nm between intrinsic homogeneous and extrinsic domain switching mechanisms.

scholarly journals Global spectroscopy of the water monomer

2012 ◽  
Vol 370 (1968) ◽  
pp. 2728-2748 ◽  
Author(s):  
Oleg L. Polyansky ◽  
Nikolay F. Zobov ◽  
Irina I. Mizus ◽  
Lorenzo Lodi ◽  
Sergei N. Yurchenko ◽  
...  
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Configuration Interaction ◽  
Basis Set ◽  
Maximum Deviation ◽  
High Resolution Spectrum ◽  
Dissociation Limit ◽  
Relativistic Energy ◽  
Interaction Technique ◽  
Semi Empirical

Given the large energy required for its electronic excitation, the most important properties of the water molecule are governed by its ground potential energy surface (PES). Novel experiments are now able to probe this surface over a very extended energy range, requiring new theoretical procedures for their interpretation. As part of this study, a new, accurate, global spectroscopic-quality PES and a new, accurate, global dipole moment surface are developed. They are used for the computation of the high-resolution spectrum of water up to the first dissociation limit and beyond as well as for the determination of Stark coefficients for high-lying states. The water PES has been determined by combined ab initio and semi-empirical studies. As a first step, a very accurate, global, ab initio PES was determined using the all-electron, internally contracted multi-reference configuration interaction technique together with a large Gaussian basis set. Scalar relativistic energy corrections are also determined in order to move the energy determinations close to the relativistic complete basis set full configuration interaction limit. The electronic energies were computed for a set of about 2500 geometries, covering carefully selected configurations from equilibrium up to dissociation. Nuclear motion computations using this PES reproduce the observed energy levels up to 39 000 cm −1 with an accuracy of better than 10 cm −1 . Line positions and widths of resonant states above dissociation show an agreement with experiment of about 50 cm −1 . An improved semi-empirical PES is produced by fitting the ab initio PES to accurate experimental data, resulting in greatly improved accuracy, with a maximum deviation of about 1 cm −1 for all vibrational band origins. Theoretical results based on this semi-empirical surface are compared with experimental data for energies starting at 27 000 cm −1 , going all the way up to dissociation at about 41 000 cm −1 and a few hundred wavenumbers beyond it.

Force field for in-plane vibrations of terephthalonitrile

1989 ◽  
Vol 54 (1) ◽  
pp. 18-27 ◽  
Author(s):  
Juan F. Arenas ◽  
Juan I. Marcos ◽  
Francisco J. Ramírez
Keyword(s):  
Experimental Data ◽  
Force Field ◽  
Normal Coordinates ◽  
Internal Coordinates ◽  
Isotopic Shifts ◽  
Quadratic Force Field ◽  
Semi Empirical

The general quadratic force field for the in-plane vibrations of terephthalonitrile was calculated by the semi-empirical MINDO/3 method. This force field was refined to the frequencies observed experimentally for terephthalonitrile and isotopic shifts of terephthalonitrile-[15N2]. The refined frequencies reproduce the experimental data with errors less than 0.5%. The normal coordinates and the force field in internal coordinates were also calculated from the refined field.

scholarly journals Local Structuring of Diketopyrrolopyrrole (DPP)-based Oligomers from Molecular Dynamics Simulations

2021 ◽  
Author(s):  
Maryam Reisjalali ◽  
J. Javier Burgos-Marmol ◽  
Rex Manurung ◽  
Alessandro Troisi
Keyword(s):  
Experimental Data ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
High Mobility ◽  
Semiconducting Polymers ◽  
Microscopic Structure ◽  
Dynamics Simulations

The microscopic structure of high mobility semiconducting polymers is known to be essential for their performance but it cannot be easily deduced from the available experimental data. A series of...

Convective Losses From Cavity Solar Receivers—Comparisons Between Analytical Predictions and Experimental Results

1983 ◽  
Vol 105 (1) ◽  
pp. 29-33 ◽  
Author(s):  
A. M. Clausing
Keyword(s):  
Experimental Data ◽  
Experimental Evidence ◽  
Analytical Model ◽  
Excellent Agreement ◽  
Experimental Results ◽  
Simple Analytical Model ◽  
Refined Model ◽  
Wall Area

Cavity solar receivers are generally believed to have higher thermal efficiencies than external receivers due to reduced losses. A simple analytical model was presented by the author which indicated that the ability to heat the air inside the cavity often controls the convective loss from cavity receivers. Thus, if the receiver contains a large amount of inactive hot wall area, it can experience a large convective loss. Excellent experimental data from a variety of cavity configurations and orientations have recently become available. These data provided a means of testing and refining the analytical model. In this manuscript, a brief description of the refined model is presented. Emphasis is placed on using available experimental evidence to substantiate the hypothesized mechanisms and assumptions. Detailed comparisons are given between analytical predictions and experimental results. Excellent agreement is obtained, and the important mechanisms are more clearly delineated.

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