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In this paper, we present a mean-field model of the spin-magnetization coupling in ferromagnetic materials. The model includes non-isotropic diffusion for spin dynamics, which is crucial in capturing strong spin-magnetization coupling. The derivation is based on a moment closure of the quantum spinor dynamics, coupled to magnetization dynamics via the(More)
We study the accuracy of the divide-and-conquer method for electronic structure calculations. The analysis is conducted for a prototypical subdomain problem in the method. We prove that the pointwise difference between electron densities of the global system and the subsystem decays exponentially as a function of the distance away from the boundary of the(More)
In this paper, we develop a mean-field model for describing the dynamics of spin transfer torque in multilayered ferromagnetic media. Specifically, we use the techniques of Wigner transform and moment closure to connect the underlying physics at different scales, and reach a macroscopic model for the dynamics of spin coupled with the magnetization within(More)
Complex quantum systems arise in the description of matter at microscopic and nanoscopic scales. The mathematical formulation and the efficient numerical simulation of such systems is a notoriously difficult problem. An interplay between mathematical analysis and numerical simulations is usually needed in order to obtain a detailed understanding. Goals To(More)
The heptamethylbenzenium cation (heptaMB(+)) has been speculated to be one of the most important active intermediates involved in the "hydrocarbon pool" mechanism of methanol-to-olefin (MTO) conversion. By the use of DNL-6, a newly synthesized SAPO-type molecular sieve with large cavities, heptaMB(+) has for the first time been directly observed during(More)
Carbenium ions in zeolites: Two important carbenium ions have been observed for the first time under working conditions of the methanol-to-olefins (MTO) reaction over chabazite zeolites using (13) C NMR spectroscopy. Their crucial roles in the MTO reaction cycles have been demonstrated by combining experiments and theoretical calculations.
By means of a many-body van der Waals (vdW)-corrected density functional theory approach, the atomic-scale friction of a prototypical tip-substrate system consisting of an Si tip and a graphene substrate is studied. In a loading-sliding process, the tip-substrate distance is found to be essential for nanofrictional behavior, through determining the(More)
The methanol-to-olefins (MTO) process is becoming the most important non-petrochemical route for the production of light olefins from coal or natural gas. Maximizing the generation of the target products, ethene and propene, and minimizing the production of byproducts and coke, are major considerations in the efficient utilization of the carbon resource of(More)