scholarly journals On-the-fly ab initio semiclassical dynamics: Identifying degrees of freedom essential for emission spectra of oligothiophenes

2014 ◽  
Vol 140 (24) ◽  
pp. 244114 ◽  
Author(s):  
Marius Wehrle ◽  
Miroslav Šulc ◽  
Jiří Vaníček
Keyword(s):  
Ab Initio ◽  
Degrees Of Freedom ◽  
Emission Spectra ◽  
Semiclassical Dynamics

Quantum simulations

2017 ◽  
Author(s):  
Michael P. Allen ◽  
Dominic J. Tildesley
Keyword(s):  
Ab Initio ◽  
Quantum Monte Carlo ◽  
Degrees Of Freedom ◽  
Small Region ◽  
Time Correlation ◽  
Ab Initio Molecular Dynamics ◽  
Classical Dynamics ◽  
Integral Methods ◽  
Quantum Time ◽  
Low Mass

This chapter covers the introduction of quantum mechanics into computer simulation methods. The chapter begins by explaining how electronic degrees of freedom may be handled in an ab initio fashion and how the resulting forces are included in the classical dynamics of the nuclei. The technique for combining the ab initio molecular dynamics of a small region, with classical dynamics or molecular mechanics applied to the surrounding environment, is explained. There is a section on handling quantum degrees of freedom, such as low-mass nuclei, by discretized path integral methods, complete with practical code examples. The problem of calculating quantum time correlation functions is addressed. Ground-state quantum Monte Carlo methods are explained, and the chapter concludes with a forward look to the future development of such techniques particularly to systems that include excited electronic states.

scholarly journals Hidden Nambu mechanics II: Quantum/semiclassical dynamics

2019 ◽  
Vol 2019 (12) ◽  
Author(s):  
Atsushi Horikoshi
Keyword(s):  
Time Evolution ◽  
Quantum Dynamics ◽  
Degrees Of Freedom ◽  
Hamiltonian Dynamics ◽  
Extended Phase ◽  
Nambu Mechanics ◽  
Mechanical Structure ◽  
Wave Packet Dynamics ◽  
Semiclassical Dynamics ◽  
Metastable Potential

Abstract Nambu mechanics is a generalized Hamiltonian dynamics characterized by an extended phase space and multiple Hamiltonians. In a previous paper [Prog. Theor. Exp. Phys. 2013, 073A01 (2013)] we revealed that the Nambu mechanical structure is hidden in Hamiltonian dynamics, that is, the classical time evolution of variables including redundant degrees of freedom can be formulated as Nambu mechanics. In the present paper we show that the Nambu mechanical structure is also hidden in some quantum or semiclassical dynamics, that is, in some cases the quantum or semiclassical time evolution of expectation values of quantum mechanical operators, including composite operators, can be formulated as Nambu mechanics. We present a procedure to find hidden Nambu structures in quantum/semiclassical systems of one degree of freedom, and give two examples: the exact quantum dynamics of a harmonic oscillator, and semiclassical wave packet dynamics. Our formalism can be extended to many-degrees-of-freedom systems; however, there is a serious difficulty in this case due to interactions between degrees of freedom. To illustrate our formalism we present two sets of numerical results on semiclassical dynamics: from a one-dimensional metastable potential model and a simplified Henon–Heiles model of two interacting oscillators.

Ab Initio Stochastic Optimization of Conformational and Many-Body Degrees of Freedom

2003 ◽  
Vol 43 (6) ◽  
pp. 1820-1828 ◽  
Author(s):  
Scott A. McMillan ◽  
Ned C. Haubein ◽  
Randall Q. Snurr ◽  
Linda J. Broadbelt
Keyword(s):  
Stochastic Optimization ◽  
Ab Initio ◽  
Degrees Of Freedom ◽  
Many Body

AB INITIO CALCULATION OF $^5_\Lambda {\rm He}$ WITH EXPLICIT Σ ADMIXTURE

2003 ◽  
Vol 18 (02n06) ◽  
pp. 139-142
Author(s):  
H. NEMURA ◽  
Y. AKAISHI ◽  
Y. SUZUKI
Keyword(s):  
Ab Initio ◽  
Internal Energy ◽  
Ab Initio Calculation ◽  
Degrees Of Freedom ◽  
Bound State ◽  
Bound State Solution ◽  
Expectation Value ◽  
Variational Calculations ◽  
Energy Expectation ◽  
Energy Expectation Value

Variational calculations for s-shell hypernuclei are performed by explicitly including Σ degrees of freedom. Two sets of YN interactions (D2 and SC97e(S)) are used. The bound-state solution of [Formula: see text] is obtained by using each of YN potentials, and a large energy expectation value of the tensor ΛN - ΣN transition part is found by using the SC97e(S). The internal energy of 4 He subsystem changes a lot by the presence of a Λ particle with the strong tensor ΛN - ΣN transition potential.

The absorption and emission spectra of HD in the vacuum ultraviolet

1976 ◽  
Vol 54 (5) ◽  
pp. 525-567 ◽  
Author(s):  
I. Dabrowski ◽  
G. Herzberg
Keyword(s):  
Absorption Spectrum ◽  
Ab Initio ◽  
Excited States ◽  
Vacuum Ultraviolet ◽  
Emission Spectra ◽  
Dissociation Limit ◽  
Infinite Mass ◽  
Ab Initio Theory ◽  
Vibrational Constants ◽  
Weak Transitions

The absorption spectrum of HD has been studied under high resolution in the vacuum ultraviolet to 840 Å, the emission spectrum to 1000 Å. The analysis of the latter gives accurate rotational constants and vibrational intervals of the ground state right up to the dissociation limit. Comparing these experimental data with calculations from ab initio theory, agreement to the same extent as was previously found for H2 and D2 is obtained. Extrapolation of the obs. – calc. values from H2 and D2 to infinite mass yields agreement with the recently revised theoretical values to within less than 0.1 for v < 7 and less than 0.5 cm−1 for the whole range of observed v values. The deviations for finite mass (H2 and D2) are clearly due to the non-adiabatic corrections neglected in the ab initio calculations. The results for HD are not halfway between H2 and D2 but are closer to H2. This apparent anomaly can be quantitatively accounted for, on the basis of recent calculations of Wolniewicz, by the effect of additional nonadiabatic corrections caused by the excited Σu states which in HD, unlike H2 and D2, can interact with the ground state.The rotational and vibrational constants of the excited states B1Σu+, C1Πu, and B′1Σu+ show somewhat larger deviations from ab initio values ranging for v0v from 5 to 120 cm−1, just as for H2 and D2. The electronic isotope shift of HD lies approximately half-way between the values of H2 and D2 as expected. In addition to the B–X, C–X, and B′–X systems the absorption spectrum of HD, unlike that of H2 and D2, shows an extensive progression of weak transitions to the double minimum state EF1Σg+ and a few very weak transitions to the G1Σg+ and I1Πg states. For the EF state both levels in the outer minimum (F) and levels above the maximum are observed. The correlation of the six excited states B, C, B′, EF, G, and I to the two close-lying dissociation limits corresponding to H + D* and H* + D is briefly discussed.

Ab initio simulation of pyrene spectra in water matrices

RSC Advances ◽  
2014 ◽  
Vol 4 (79) ◽  
pp. 42054-42065 ◽  
Author(s):  
A. Ya. Freidzon ◽  
R. R. Valiev ◽  
A. A. Berezhnoy
Keyword(s):  
Ab Initio ◽  
Emission Spectra ◽  
Large Cluster ◽  
Water Molecules ◽  
Ab Initio Simulation ◽  
Absorption And Emission ◽  
Water Ice ◽  
Absorption And Emission Spectra ◽  
Explicit Water

The absorption and emission spectra of free pyrene and pyrene in a water ice matrix were simulated ab initio with their vibronic profiles. Water ice was mimicked by a large cluster of explicit water molecules.

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