Current reversals and metastable states in the infinite Bose-Hubbard chain with local particle loss

We present an algorithm which combines the quantum trajectory approach to open quantum systems with a density-matrix renormalization group scheme for infinite one-dimensional lattice systems. We apply this method to investigate the long-time dynamics in the Bose-Hubbard model with local particle loss starting from a Mott-insulating initial state with one boson per site. While the short-time dynamics can be described even quantitatively by an equation of motion (EOM) approach at the mean-field level, many-body interactions lead to unexpected effects at intermediate and long times: local particle currents far away from the dissipative site start to reverse direction ultimately leading to a metastable state with a total particle current pointing away from the lossy site. An alternative EOM approach based on an effective fermion model shows that the reversal of currents can be understood qualitatively by the creation of holon-doublon pairs at the edge of the region of reduced particle density. The doublons are then able to escape while the holes move towards the dissipative site, a process reminiscent---in a loose sense---of Hawking radiation

Solvent Effect and Hydrogen Bond Interaction on Tautomerism, Vibrational Frequencies, and Raman Spectra of Guanine: A Density Functional Theoretical Study

Stable structures and Raman spectra of guanine have been investigated by density functional theory (DFT). Focusing on solvent effect and hydrogen bonding interaction, we have calculated the two keto-amino tautomers G17K and G19K as well as their guanine–water complexes and tetramers. The results show G17K is more stable than G19K in the gas phase, whereas in polar solvents G19K dominates. The vibrational fundamentals of G17K have been reassigned based on normal-mode analysis, since the previous assignment was limited to the G19K only. In the Raman spectra, the modes of the ring breathing vibration and those in the fingerprint region (from 1000 to 1600 cm^–1) affected by the solvent effect and the hydrogen bonding interaction dramatically. The band at 1163 cm^–1 of G17K in gas has a large blue shift when water molecule forms hydrogen bonds with N₇–H₁₆ and C₆O₁₃ sites. The blue shift can be explained by the influence of hydrogen bonding interaction along with shortening the N₁–C₆ bond distance. In addition, the dominant existing tautomer in polycrystalline and powder guanine is proposed to be G17K, whose calculated vibrational frequencies agree with the experimental Raman spectra reported before

Structural and Charge Sensitivity of Surface-Enhanced Raman Spectroscopy of Adenine on Silver Surface: A Quantum Chemical Study

The interaction of adenine with silver surfaces has been investigated using density functional method. Two isomers of N9H and N7H were included to model surface species. Considering the complexity of silver surfaces in surface-enhanced Raman spectroscopy, neutral and positive silver clusters were used to mimic the substrate. Following the bonding principle, we consider adenine-approached silver clusters in different configurations and their relation to the Raman spectra. For neutral adenine Ag_<i>n</i> (<i>n</i> = 4, 7, and 9) complexes, N9H–Ag_<i>n</i> complexes are more stable than N7H–Ag_<i>n</i> ones. The corresponding Raman spectra strongly depended on the structure of adenine and the adsorption sites. Moreover, we find N7H interacts with one positively charged silver cluster via N3 and N9 at the same time as the most stable surface complex, which can reproduce the experimental surface Raman spectra of adenine well on silver surfaces