Continuous matrix product states with periodic boundary conditions and an application to atomtronics

We introduce a time evolution algorithm for one-dimensional quantum field theories with periodic boundary conditions. This is done by applying the Dirac-Frenkel time-dependent variational principle to the set of translational invariant continuous matrix product stateswith periodic boundary conditions. Moreover, the ansatz is accompanied with additional boundary degrees of freedom to study quantum impurity problems. The algorithm allows for a cutoff in the spectrum of the transfer matrix and thus has an efficient computational scaling. In particular we study the prototypical example of an atomtronic system-an interacting Bose gas rotating in a ring shaped trap in the presence of a localized barrier potential

Simulation of Heme using DFT+U: a step toward accurate spin-state energetics

We investigate the DFT+U approach as a viable solution to describe the low-lying states of ligated and unligated iron heme complexes. Besides their central role in organometallic chemistry, these compounds represent a paradigmatic case where LDA, GGA, and common hybrid functionals fail to reproduce the experimental magnetic splittings. In particular, the imidazole pentacoordinated heme is incorrectly described as a triplet by all usual DFT flavors. In this study we show that a U parameter close to 4 eV leads to spin transitions and molecular geometries in quantitative agreement with experiments, and that DFT+U represents an appealing tool in the description of iron porphyrin complexes, at a much reduced cost compared to correlated quantum-chemistry methods. The possibility of obtaining the U parameter from first-principles is explored through a self-consistent linear-response formulation. We find that this approach, which proved to be successful in other iron systems, produces in this case some overestimation with respect to the optimal values of U.Comment: To be published in The Journal of Physical Chemistry B 30 pages, 15 figure

Density functional theory in transition-metal chemistry: a self-consistent Hubbard U approach

Transition-metal centers are the active sites for many biological and inorganic chemical reactions. Notwithstanding this central importance, density-functional theory calculations based on generalized-gradient approximations often fail to describe energetics, multiplet structures, reaction barriers, and geometries around the active sites. We suggest here an alternative approach, derived from the Hubbard U correction to solid-state problems, that provides an excellent agreement with correlated-electron quantum chemistry calculations in test cases that range from the ground state of Fe$_2$ and Fe$_2^-$ to the addition-elimination of molecular hydrogen on FeO$^+$. The Hubbard U is determined with a novel self-consistent procedure based on a linear-response approach.Comment: 5 pages, 3 figures, Phys. Rev. Lett., in pres

In situ neutron diffraction to investigate the solid-state synthesis of Ni-rich cathode materials

Studying chemical reactions in real time can provide unparalleled insight into the evolution of intermediate species and can provide guidance to optimize the reaction conditions. For solid-state synthesis reactions, powder diffraction has been demonstrated as an effective tool for resolving the structural evolution taking place upon heating. The synthesis of layered Ni-rich transition-metal oxides at a large scale (grams to kilograms) is highly relevant as these materials are commonly employed as cathodes for Li-ion batteries. In this work, in situ neutron diffraction was used to monitor the reaction mechanism during the high-temperature synthesis of Ni-rich cathode materials with a varying ratio of Ni:Mn from industrially relevant hydroxide precursors. Rietveld refinement was further used to model the observed phase evolution during synthesis and compare the behaviour of the materials as a function of temperature. The results presented herein confirm the suitability of in situ neutron diffraction to investigate the synthesis of batches of several grams of electrode materials with well-controlled stoichiometry. Furthermore, monitoring the structural evolution of the mixtures with varying Ni:Mn content in real time reveals a delayed onset of li­thia­tion as the Mn content is increased, necessitating the use of higher annealing temperatures to achieve layering

Recyclable and Robust Optical Nanoprobes with Engineered Enzymes for Sustainable Serodiagnostics

Recyclable fluorescence assays that can be stored at room temperature would greatly benefit biomedical diagnostics by bringing sustainability and cost-efficiency, especially for point-of-care serodiagnostics in developing regions. Here, a general strategy is proposed to generate recyclable fluorescent probes by using engineered enzymes with enhanced thermo-/chemo-stability, which maintains an outstanding serodiagnostic performance (accuracy >95%) after 10 times of recycling as well as after storage at elevated temperatures (37 °C for 10 days). With these three outstanding properties, recyclable fluorescent probes can be designed to detect various biomarkers of clinical importance by using different enzymes