Quantum information analysis of electronic states at different molecular structures

We have studied transition metal clusters from a quantum information theory perspective using the density-matrix renormalization group (DMRG) method. We demonstrate the competition between entanglement and interaction localization. We also discuss the application of the configuration interaction based dynamically extended active space procedure which significantly reduces the effective system size and accelerates the speed of convergence for complicated molecular electronic structures to a great extent. Our results indicate the importance of taking entanglement among molecular orbitals into account in order to devise an optimal orbital ordering and carry out efficient calculations on transition metal clusters. We propose a recipe to perform DMRG calculations in a black-box fashion and we point out the connections of our work to other tensor network state approaches

Reliable estimation of prediction uncertainty for physico-chemical property models

The predictions of parameteric property models and their uncertainties are sensitive to systematic errors such as inconsistent reference data, parametric model assumptions, or inadequate computational methods. Here, we discuss the calibration of property models in the light of bootstrapping, a sampling method akin to Bayesian inference that can be employed for identifying systematic errors and for reliable estimation of the prediction uncertainty. We apply bootstrapping to assess a linear property model linking the 57Fe Moessbauer isomer shift to the contact electron density at the iron nucleus for a diverse set of 44 molecular iron compounds. The contact electron density is calculated with twelve density functionals across Jacob's ladder (PWLDA, BP86, BLYP, PW91, PBE, M06-L, TPSS, B3LYP, B3PW91, PBE0, M06, TPSSh). We provide systematic-error diagnostics and reliable, locally resolved uncertainties for isomer-shift predictions. Pure and hybrid density functionals yield average prediction uncertainties of 0.06-0.08 mm/s and 0.04-0.05 mm/s, respectively, the latter being close to the average experimental uncertainty of 0.02 mm/s. Furthermore, we show that both model parameters and prediction uncertainty depend significantly on the composition and number of reference data points. Accordingly, we suggest that rankings of density functionals based on performance measures (e.g., the coefficient of correlation, r2, or the root-mean-square error, RMSE) should not be inferred from a single data set. This study presents the first statistically rigorous calibration analysis for theoretical Moessbauer spectroscopy, which is of general applicability for physico-chemical property models and not restricted to isomer-shift predictions. We provide the statistically meaningful reference data set MIS39 and a new calibration of the isomer shift based on the PBE0 functional.Comment: 49 pages, 9 figures, 7 table

Spin Transition Sensors Based on β-Amino-Acid 1,2,4-Triazole Derivative

A β-aminoacid ester was successfully derivatized to yield to 4H-1,2-4-triazol-4-yl-propionate (βAlatrz) which served as a neutral bidentate ligand in the 1D coordination polymer [Fe(βAlatrz)3](CF3SO3)2·0.5H2O (1·0.5H2O). The temperature dependence of the high-spin molar fraction derived from 57Fe Mossbauer spectroscopy recorded on cooling below room temperature reveals an exceptionally abrupt single step transition between high-spin and low-spin states with a hysteresis loop of width 4 K (Tc↑ = 232 K and Tc↓ = 228 K) in agreement with magnetic susceptibility measurements. The material presents striking reversible thermochromism from white, at room temperature, to pink on quench cooling to liquid nitrogen, and acts as an alert towards temperature variations. The phase transition is of first order, as determined by differential scanning calorimetry, with transition temperatures matching the ones determined by SQUID and Mössbauer spectroscopy. The freshly prepared sample of 1·0.5H2O, dried in air, was subjected to annealing at 390 K, and the obtained white compound [Fe(βAlatrz)3](CF3SO3)2 (1) was found to exhibit a similar spin transition curve however much temperature was increased by (Tc↑ = 252 K and Tc↓ = 248 K). The removal of lattice water molecules from 1·0.5H2O is not accompanied by a change of the morphology and of the space group, and the chain character is preserved. However, an internal pressure effect stabilizing the low-spin state is evidenced

Interplay between lattice, orbital, and magnetic degrees of freedom in the chain-polymer Cu(II) breathing crystals

The chain-polymer Cu(II) breathing crystals C21H19CuF12N4O6 were studied using the x-ray diffraction and ab initio band structure calculations. We show that the crystal structure modification at T=146 K, associated with the spin crossover transition, induces the changes of the orbital order in half of the Cu sites. This in turn results in the switch of the magnetic interaction sign in accordance with the Goodenough-Kanamori-Andersen theory of the coupling between the orbital and spin degrees of freedom.Comment: 6 pages, 7 figure

Collective effects in spin-crossover chains with exchange interaction

The collective properties of spin-crossover chains are studied. Spin-crossover compounds contain ions with a low-spin ground state and low lying high-spin excited states and are of interest for molecular memory applications. Some of them naturally form one-dimensional chains. Elastic interaction and Ising exchange interaction are taken into account. The transfer-matrix approach is used to calculate the partition function, the fraction of ions in the high-spin state, the magnetization, susceptibility, etc., exactly. The high-spin-low-spin degree of freedom leads to collective effects not present in simple spin chains. The ground-state phase diagram is mapped out and compared to the case with Heisenberg exchange interaction. The various phases give rise to characteristic behavior at nonzero temperatures, including sharp crossovers between low- and high-temperature regimes. A Curie-Weiss law for the susceptibility is derived and the paramagnetic Curie temperature is calculated. Possible experiments to determine the exchange coupling are discussed.Comment: 9 pages, 13 color figures, published versio

Infrared study of spin crossover Fe-picolylamine complex

Infrared (IR) absorption spectroscopy has been used to probe the evolution of microscopic vibrational states upon the temperature- and photo-induced spin crossovers in [Fe(2-picolylamine)3]Cl2EtOH (Fe-pic). To overcome the small sizes and the strong IR absorption of the crystal samples used, an IR synchrotron radiation source and an IR microscope have been used. The obtained IR spectra of Fe-pic show large changes between high-spin and low-spin states for both the temperature- and the photo- induced spin crossovers. Although the spectra in the temperature- and photo-induced high-spin states are relatively similar to each other, they show distinct differences below 750 cm-1. This demonstrates that the photo-induced high-spin state involves microscopically different characters from those of the temperature-induced high-spin state. The results are discussed in terms of local pressure and structural deformations within the picolylamine ligands, and in terms of their possible relevance to the development of macroscopic photo-induced phase in Fe-pic.Comment: 6 pages (text) and 6 figures,submitted to J. Phys. Soc. Jp

Photoinduced magnetism and random magnetic anisotropy in organic-based magnetic semiconductor V(TCNE)(x) films, for x similar to 2

The V(TCNE)(x), x similar to 2 is an organic-based amorphous ferrimagnet, whose magnetic behavior is significantly affected in the low field regime by the random magnetic anisotropy. It was determined that this material has thermally reversible persistent change in both magnetization and conductivity driven by the optical excitation. Here, we report results of a ferrimagnetic resonance study of the photoinduced magnetism in V(TCNE)(x) film. Upon optical excitation (lambda similar to 457.9 nm), the ferrimagnetic resonance spectra display substantial changes in their linewidths and line shifts, which reflect a substantial increase in the random magnetic anistropy. The results reflect the role of magnetic anisotropy in disordered magnets and suggest a novel mechanism of photoinduced magnetism in V(TCNE)(x) induced by the increased structural disorder in the system.open201

A Unified Theoretical Description of the Thermodynamical Properties of Spin Crossover with Magnetic Interactions

After the discovery of the phenomena of light-induced excited spin state trapping (LIESST), the functional properties of metal complexes have been studied intensively. Among them, cooperative phenomena involving low spin-high spin (spin-crossover) transition and magnetic ordering have attracted interests, and it has become necessary to formulate a unified description of both phenomena. In this work, we propose a model in which they can be treated simultaneously by extending the Wajnflasz-Pick model including a magnetic interaction. We found that this new model is equivalent to Blume-Emery-Griffiths (BEG) Hamiltonian with degenerate levels. This model provides a unified description of the thermodynamic properties associated with various types of systems, such as spin-crossover (SC) solids and Prussian blue analogues (PBA). Here, the high spin fraction and the magnetization are the order parameters describing the cooperative phenomena of the model. We present several typical temperature dependences of the order parameters and we determine the phase diagram of the system using the mean-field theory and Monte Carlo simulations. We found that the magnetic interaction drives the SC transition leading to re-entrant magnetic and first-order SC transitions.Comment: 30pages, 11figure

Switching dynamics between metastable ordered magnetic state and nonmagnetic ground state - A possible mechanism for photoinduced ferromagnetism -

By studying the dynamics of the metastable magnetization of a statistical mechanical model we propose a switching mechanism of photoinduced magnetization. The equilibrium and nonequilibrium properties of the Blume-Capel (BC) model, which is a typical model exhibiting metastability, are studied by mean field theory and Monte Carlo simulation. We demonstrate reversible changes of magnetization in a sequence of changes of system parameters, which would model the reversible photoinduced magnetization. Implications of the calculated results are discussed in relation to the recent experimental results for prussian blue analogs.Comment: 12 pages, 13 figure