Semiclassical and quantum polarons in crystaline acetanilide

Crystalline acetanilide is a an organic solid with peptide bond structure similar to that of proteins. Two states appear in the amide I spectral region having drastically different properties: one is strongly temperature dependent and disappears at high temperatures while the other is stable at all temperatures. Experimental and theoretical work over the past twenty five years has assigned the former to a selftrapped state while the latter to an extended free exciton state. In this article we review the experimental and theoretical developments on acetanilide paying particular attention to issues that are still pending. Although the interpretation of the states is experimentally sound, we find that specific theoretical comprehension is still lacking. Among the issues that that appear not well understood is the effective dimensionality of the selftrapped polaron and free exciton states.Comment: 28 pages 13 figure

Femtosecond IR Pump-Probe Spectroscopy of Nonlinear Energy Localization in Protein Models and Model Proteins

This paper reviews our experimental and theoretical efforts toward understanding vibrational self-trapping of the amide I and N-H mode of crystalline acetanilide (ACN), other similar hydrogen-bonded crystals, as well as of model peptides. In contrast to previous works, we used nonlinear IR spectroscopy as the experimental tool, which is specifically sensitive to the anharmonic contributions of the intramolecular interactions (as the nonlinear IR response of set of harmonic oscillators vanishes exactly). Our work reconfirms the previous assignment of the two bands of the amide I mode of ACN as being a self-trapped and a free exciton state, but in addition also establishes the lifetimes of these states and identifies the relevant phonons. Furthermore, we provide evidence for vibrationally self-trapped states also in model α-helices. However, given the short lifetime, any biological relevance in the sense of Davydov's initial proposal can probably be ruled ou

Velocity echoes in water

A three-point velocity correlation function v(t(1) + t(2))v2(t(1))v(0) is introduced for a better understanding of the recent 2D-Raman-THz spectroscopy of the intermolecular degrees of freedoms of water and aqueous salt solutions. This correlation function reveals echoes in the presence of inhomogeneous broadening, which are coined velocity echoes. In analogy to the well-known two-point velocity correlation function v(t)v(0), it reflects the density of states (DOS) of the system under study without having to amend them with transition dipoles and transition polarizabilities. The correlation function can be calculated from equilibrium trajectories and converges extremely quickly. After deriving the theory, the information content of the three-point velocity correlation function is first tested based on a simple harmonic oscillator model with Langevin dynamics. Subsequently, velocity echoes of TIP4P/2005 water are calculated as a function of temperature, covering ambient conditions, the supercooled regime and amorphous ice, as well as upon addition of various salts. The experimentally observed trends can be reproduced qualitatively with the help of computationally very inexpensive molecular dynamics simulations

CRYPTOCURRENCIES, STABLECOINS AND CENTRAL BANK DIGITAL CURRENCIES: THE IMPACT OF TRUST AND PERCEIVED RISK

Financial technology is undergoing rapid developments with the arrival of cryptocurrencies, the introduction of stablecoins, and more recently the discussion surrounding central bank digital currencies. The adoption of these technologies has received significant attention, but there has not yet been any research as to how the adoption factors for the three currencies differ, given their inherent similarities. This paper proposes to estimate the effect of trust and perceived risk on the adoption intention of the three aforementioned payment systems by creating three closely-matched questionnaires for each digital currency. This will enable us to estimate the effects of risk and trust in a way that makes it possible to compare the effect sizes for the different technologies, and can help evaluate whether a reduction of perceived market risk is sufficient for cryptocurrency adoption, and whether backing by the central bank may confer more benefits to adoption than the trustlessness touted for cryptocurrencies

Acceptance Factors for Cryptocurrencies as Payment Systems

The adoption of cryptocurrencies and blockchain technologies is an active field of research in information systems, looking at the promise and issues hampering the arrival of cryptocurrencies as a general means of payment. However, an overwhelming number of papers only look at existing users and usually limit themselves to a single cryptocurrency, mostly Bitcoin. This paper adds to the body of research by creating a taxonomy of features for cryptocurrencies as payment systems, and conducting a user study with over 500 participants asking what features are most relevant for the adoption of a cryptocurrency. We identify cost-effectiveness and data confidentiality as crucial for potential users, but also find that these two factors are followed by a wealth of convenience features that have found less emphasis in present cryptocurrency implementations

Versatile Femtosecond Laser Synchronization for Multiple-Timescale Transient IR Spectroscopy

Several ways to electronically synchronize different types of amplified femtosecond laser systems are presented, based on a single freely programmable electronics hardware: Arbitrary-detuning asynchronous optical sampling, as well as actively locking two femtosecond laser oscillators, albeit not necessarily to the same round-trip frequency. They allow us to rapidly probe a very wide range of timescales, from picoseconds to potentially seconds, in a single transient absorption experiment without the need to move any delay stage. Experiments become possible that address a largely unexplored aspect of many photochemical reactions, in particular in the context of photo-catalysis as well as photoactive proteins, where an initial femtosecond trigger very often initiates a long-lasting cascade of follow-up processes. The approach is very versatile, and allows us to synchronize very different lasers, such as a Ti:Sa amplifier and a 100~kHz Yb-laser system. The jitter of the synchronisation, and therewith the time-resolution in the transient experiment, lies in the range from 1~ps to 3~ps, depending on the method. For illustration, transient IR measurements of the excited state solvation and decay of a metal carbonyl complex as well as the full reaction cycle of bacteriorhodopsin are shown. The pros and cons of the various methods are discussed, with regard to the scientific question one might want to address, and also with regard to the laser systems that might be already existent in a laser lab

Ultrafast Dynamics of Liquid Water and Ice

In the present contribution we summarize our observations concerning the ultrafast non-equilibrium dynamics of water, in both the liquid and crystalline phase. Our experimental tool is two-dimensional infrared (2D IR) spectroscopy, which combines structural information on a molecular level with femtosecond time resolution. In the case of liquid and supercooled water we are able to extract the timescales of hydrogen bonding dynamics, whereas in the ice form we can probe the change of the hydrogen bond properties under excitation and observe the influence of intermolecular mode excitations in the crystal

An efficient water force field calibrated against intermolecular THz and Raman spectra

A polarizable water model is presented which has been calibrated against experimental THz and Raman spectra of bulk water. These low-frequency spectra directly probe the dynamics, and thereby intermolecular interactions, on time scales relevant to molecular motions. The model is based on the TL4P force field developed recently by Tavan and co-workers [J. Phys. Chem. B 117 , 9486 (2013)], which has been designed to be transferable between different environments; in particular, to correctly describe the electrostatic properties of both the isolated water molecule in the gas-phase and the liquid water at ambient conditions. Following this design philosophy, TL4P was amended with charge transfer across hydrogen-bonded dimers as well as an anisotropic polarizability in order to correctly reproduce the THz and Raman spectra. The thermodynamic and structural properties of the new model are of equal quality as those of TL4P, and at the same time, an almost quantitative agreement with the spectroscopic data could be achieved. Since TL4P is a rigid model with a single polarizable site, it is computationally very efficient, while the numerical overhead for the addition of charge transfer and the anisotropic polarizability is minor. Overall, the model is expected to be well suited for, e.g., large scale simulations of 2D-Raman-THz spectra or biomolecular simulations