36 research outputs found
Atomic and molecular complex resonances from real eigenvalues using standard (hermitian) electronic structure calculations
Complex eigenvalues, resonances, play an important role in large variety of
fields in physics and chemistry. For example, in cold molecular collision
experiments and electron scattering experiments, autoionizing and
pre-dissociative metastable resonances are generated. However, the computation
of complex resonance eigenvalues is difficult, since it requires severe
modifications of standard electronic structure codes and methods. Here we show
how resonance eigenvalues, positions and widths, can be calculated using the
standard, widely used, electronic-structure packages. Our method enables the
calculations of the complex resonance eigenvalues by using analytical
continuation procedures (such as Pad\'{e}). The key point in our approach is
the existence of narrow analytical passages from the real axis to the complex
energy plane. In fact, the existence of these analytical passages relies on
using finite basis sets. These passages become narrower as the basis set
becomes more complete, whereas in the exact limit, these passages to the
complex plane are closed.
As illustrative numerical examples we calculated the autoionization
resonances of helium, hydrogen anion and hydrogen molecule. We show that our
results are in an excellent agreement with the results obtained by other
theoretical methods and with available experimental results
Large Vibrationally Induced Parity Violation Effects in CHDBrI A Promising Candidate for Future Experiments
The isotopically chiral molecular ion CHDBrI is identified as an
exceptionally promising candidate for the detection of parity violation in
vibrational transitions. The largest predicted parity-violating frequency shift
reaches 1.8 Hz for the hydrogen wagging mode which has a sub-Hz natural line
width and its vibrational frequency auspiciously lies in the available laser
range. In stark contrast to this result, the parent neutral molecule is two
orders of magnitude less sensitive to parity violation. The origin of this
effect is analyzed and explained. Precision vibrational spectroscopy of
CHDBrI is feasible as it is amenable to preparation at internally low
temperatures and resistant to predissociation, promoting long interrogation
times (Landau et al.). The intersection of these properties in this molecular
ion places the first observation of parity violation in chiral molecules within
reach
Chiral molecule candidates for trapped ion spectroscopy by ab-initio calculations: from state preparation to parity violation
Parity non-conservation (PNC) due to the weak interaction is predicted to
give rise to enantiomer dependent vibrational constants in chiral molecules,
but the phenomenon has so far eluded experimental observation. The enhanced
sensitivity of molecules to physics beyond the Standard Model (BSM), has led to
substantial advances in molecular precision spectroscopy, and these may be
applied to PNC searches as well. Specifically, trapped molecular ion
experiments leverage the universality of trapping charged particles to optimize
the molecular ion species studied toward BSM searches, but in searches for PNC
only a few chiral molecular ion candidates have been proposed so far.
Importantly, viable candidates need to be internally cold and their internal
state populations should be detectable with high quantum efficiency. To this
end, we focus on molecular ions that can be created by near threshold resonant
two-photon ionization and detected via state-selective photo-dissociation. Such
candidates need to be stable in both charged and neutral chiral versions to be
amenable to these methods. Here, we present a collection of suitable chiral
molecular ion candidates we have found, including CHDBrI and CHCaBrI,
that fulfill these conditions according to our \textit{ab-initio} calculations.
We find that organo-metallic species have a low ionization energy as neutrals
and relatively high dissociation thresholds. Finally, we compute the magnitude
of the PNC values for vibrational transitions for some of these candidates. An
experimental demonstration of state preparation and readout for these
candidates will be an important milestone toward measuring PNC in chiral
molecules for the first time.Comment: 14 pages, 3 figures and supplementary informatio
Experimental signatures of the quantum-classical transition in a nanomechanical oscillator modeled as a damped driven double-well problem
We demonstrate robust and reliable signatures for the transition from quantum
to classical behavior in the position probability distribution of a damped
double-well system using the Qunatum State Diffusion approach to open quantum
systems. We argue that these signatures are within experimental reach, for
example in a doubly-clamped nanomechanical beam.Comment: Proceedings of the conference FMQT 1
Electrochemical polymerization and characterization of a functional dicarbazole conducting polymer
Abstract The electropolymerization of the unique dicarbazole monomer, 2,6-bis-carbazole-9-yl-hexanoic acid pentafluorophenyl ester, is reported. This chiral monomer possesses two carbazole units and a chiral grafting center, activated ester for covalent aminecoupling. Contrary to monocarbazole monomers unable of internal cross-linking, its specifically designed dicarbazole skeleton allowed us to obtain highly reticulated polydicarbazole films functionalized for probe coupling. Full analysis of its electrochemical polymerization revealed different oxidation potentials for the two structurally different carbazole units. The electrochemical activity of the polydicarbazole-coated electrode has been characterized in different redox electrolytes. Contacted by a model protein (BSA), this film has been easily passivated at the Rubpy 3 (PF 6 ) electrochemical window.
Electronic Structure and Spectroscopy of Nucleic Acid Bases: Ionization Energies, Ionization-Induced Structural Changes, and Photoelectron Spectra
We report high-level ab initio calculations and single-photon ionization mass spectrometry study of ionization of adenine (A), thymine (T), cytosine (C) and guanine (G). For thymine and adenine, only the lowest-energy tautomers were considered, whereas for cytosine and guanine we characterized five lowest-energy tautomeric forms. The first adiabatic and several vertical ionization energies were computed using equation-of-motion coupled-cluster method for ionization potentials with single and double substitutions. Equilibrium structures of the cationic ground states were characterized by DFT with the {omega}B97X-D functional. The ionization-induced geometry changes of the bases are consistent with the shapes of the corresponding molecular orbitals. For the lowest-energy tautomers, the magnitude of the structural relaxation decreases in the following series G > C > A > T, the respective relaxation energies being 0.41, 0.32, 0.25 and 0.20 eV. The computed adiabatic ionization energies (8.13, 8.89, 8.51-8.67 and 7.75-7.87 eV for A,T,C and G, respectively) agree well with the onsets of the photoionization efficiency (PIE) curves (8.20 {+-} 0.05, 8.95 {+-} 0.05, 8.60 {+-} 0.05 and 7.75 {+-} 0.05 eV). Vibrational progressions for the S{sub 0}-D{sub 0} vibronic bands computed within double-harmonic approximation with Duschinsky rotations are compared with previously reported experimental photoelectron spectra
Advances in Molecular Quantum Chemistry Contained in the Q-Chem 4 Program Package
A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Møller–Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube
Software for the frontiers of quantum chemistry:An overview of developments in the Q-Chem 5 package
This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange–correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear–electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an “open teamware” model and an increasingly modular design
Shaping and controlling stabilisation graphs for calculating stable complex resonance energies
Complex Energies and Transition-Dipoles for the Uracil anion Shape-type Resonances from stabilization curves via Padé
Absorption of slow moving electrons by neutral ground state nucleobases have been known to produce resonance, metastable, states. There are indications that such metastable states may play a key-role in DNA/RNA damage. Therefore, herein, we present an ab-initio, non-Hermitian investigation of the resonance positions and decay rates of the low lying shape-type states of the uracil anion. In addition, we calculate the complex transition dipoles between these resonance states. We employ the resonance via Padé (RVP) method to calculate these complex properties from real stabilization curves by analytical dilation into the complex plane. This method has al-ready been successfully applied to many small molecular systems and herein we present the first application of RVP to a medium-size system. The presented resonance energies are converged with respect to the size of the basis set and compared with previous theoretical works and experimental findings. Complex transition dipoles between the shape-type resonances are computed using the energy-converged basis set. The ability to calculate ab-initio energies and lifetimes of biologically relevant systems opens the door for studying reactions of such systems in which autoionization takes place. While the ability to also calculate their complex transition dipoles open the door for studying photo induced dynamics of such biological molecules