Spin-flip dynamics

We would like to point out that the focus in these studies was on the mechanistic aspect and the timescale involved in the dynamics after the ISC event and not on the ISC event itself. For many organic compounds, the spin-flip dynamics is in general not ultrafast (timescale of ISC is in the order of 10 s) due to the weak spin-orbit couplings [56]. The long timescale involved makes it unfeasible to simulate the ISC event itself. 

The simulation is performed in a grand canonical ensemble (GCE) where all microstates have the same volume (V), temperature and chemical potential under the periodic boundary condition to minimize a finite size effect [30, 31]. For thermal equilibrium at a fixed pu, a standard Metropolis algorithm is repetitively employed with single spin-flip dynamics [30, 31]. When equilibrium has been achieved, the lithium content (1 — 5) in the Li, 3 11204 electrode at a given pu is determined from the fraction of occupied sites. The thermodynamic partial molar quantities oflithium ions are theoretically obtained by fluctuation method [32]. The partial molar internal energy Uu at constant Vand T in the GCE is readily given by [32, 33]... 

Breaking the Curse of the Non-Dynamical Correlation Problem The Spin-Flip Method... 

Krylov, A. I., Slipchenko, L. V., and Levchenko, S. V. Breaking the Curse of the Non-dynamical Correlation Problem the Spin-Flip Method , ACS Symp. Ser., in press. 

When 7i becomes very large, the double spin-flips process becomes the fastest pathway of relaxation. In this hmit, the description in terms of effective spin units becomes also relevant for the dynamics and Eq. 33b can be identified to ... 

A small number of defects can also have a drastic effect on dynamics at low temperature, when the correlation length becomes very large. The problem of finite size scaling has been discussed by J.H. Luscombe et al. in the frame of the single-spin-flip Glauber model [30]. For an open chain of size L = na (with... 

For an external magnetic field Bo along the z direction, the electron spins are oriented parallel or antiparallel to the z direction. Modulation of the components of the local field in the xy plane due to a stochastic process then induces stochastic electron spin transitions (spin flips) that contribute to longitudinal relaxation with time constant T. For historical reasons longitudinal relaxation is often termed spin-lattice relaxation. The relaxation rate T is proportional to the spectral density /(co) of the stochastic process at the resonance frequency Mo of the transition under consideration. This spectral density is maximum for a correlation time Tc of the stochastic process that fulfils the condition wqTc = 1. As correlation times usually are a monotonic function of temperature, there is a temperature for which the relaxation rate attains a maximum and T attains a minimum. Measurements of 7] as a function of temperature can thus be used to infer the correlation time of a dynamic process. By varying the external field Bo and thus mq, the time scale can be shifted to which EPR experiments are most sensitive. 

For the dipolar relaxation mechanism, the spin lattice relaxation time is sensitive to the reorientation dynamics of the CH bond vectors. Different orientations of the CH bond result in slightly different magnetic fields at the carbon nucleus and the modulation of this field allows the spin flips to occur. When we define ecn as the unit vector along a CH bond, the second Legendre polynomial of its autocorrelation function is given by... 

High Si spin polarization obtained by dynamic nuclear polarization in microcrystalline silicon powder was reported. Unpaired electrons in this silicon powder are due to dangling bonds in the amorphous region of this intrinsically heterogeneous sample. Si nuclei in the amorphous region become polarized by forced electron-nuclear spin flips driven by off-res-onant microwave radiation while nuclei in the crystalline region are polarized by spin diffusion across crystalline boundaries. Hyperpolarized silicon microparticles have long T-1 relaxation times and could be used as tracers for MRI. 

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