Cooperativity of Spin Crossover Complexes: Combining Periodic Density Functional Calculations and Monte Carlo Simulations

The total enthalpies of the 16 different spin configurations that can be realized in the unit cell of the archetype spin crossover complex [Fe(phen)2(NCS)2] (phen=1,2-phenanthroline) were calculated applying periodic density functional theory combined with the Hubbard model and the Grimme-D2 dispersion correction (DFT+U/D2). The obtained enthalpy differences between the individual spin configurations were used to determine spin couplings of an Ising-like model and subsequent Monte Carlo simulations for this model allowed to estimate the phenomenological interaction parameter Г of the Slichter-Drickamer model, which is commonly used to describe the cooperativity of the spin transition. The calculational procedure described here, which led to an estimate of about 3 kJ/mol−1 for Г, in good agreement with experiment, may be used to predict from first principles how modifications of spin crossover complexes can change the character of the spin transition from gradual to abrupt and vice versa.

FITTING OF WATER HYDROGEN BOND ENERGY DATA WITH UNCERTAINTIES IN BOTH VARIABLES BY HELP OF ORTHONORMAL POLYNOMIALS

We generalize our previously given calculational procedure based on orthogonal polynomial expansions for curve fitting applicable to data with errors only in the dependent variable to the case when both independent and dependent variables have errors. We apply this procedure to an effect of water physics, namely water aeration, with importance also to environmental and biological issues.

The Oscillating Fluid Mechanics Method (OFMM) for Studying Oil Film Oscillation and Dynamic Characteristics of Journal Bearings

A new method to study oil film oscillation and to determine the unstable rotational speed and rotordynamic coefficients of bearings is presented. Differences between the new method called the Oscillating Fluid Mechanics Method (OFMM) and the previous method (quasi-steady state method) are discussed. Insufficiencies of the previous method are analyzed. The theory and calculational procedure of OFMM are given. Calculated results show that this new method provides significantly improved predictions.

The eddy structure in Stokes flow in a cavity

Stokes flow in a two-dimensional cavity of rectangular section, induced by the motion of one of the walls, is considered. A direct, efficient calculational procedure, based on an eigenfunction expansion, is used to study the eddy structure in the cavity. It is shown that some of the results of earlier studies are quantitatively in error. More importantly, two interesting questions, namely the extent of the symmetry of the corner eddies and their relationship to the large-eddy structure are settled. By carefully examining the rather sudden change in the main eddy structure for cavities of depth around 1.629, it is shown that the main eddies are formed by the merger of the primary corner eddies; the secondary corner eddies then become the primary corner eddies and so on. Thus, in the evolution of the large-eddy structure the corner eddies, in some sense, play the role of progenitors. This explicit prediction should be experimentally verifiable.