Statistical mechanics and thermodynamics of magnetic and dielectric systems based on magnetization and polarization fluctuations: Application of the quasi-Gaussian entropy theory
Statistical mechanics and thermodynamics of magnetic and dielectric systems based on magnetization and polarization fluctuations: Application of the quasi-Gaussian entropy theory
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DOI：
10.1063/1.1448290
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发表时间：
2002-03-15
影响因子：
4.4
通讯作者：
Di Nola, A
中科院分区：
文献类型：
--
作者：
Apol, MEF;Amadei, A;Di Nola, A
准高斯熵（QGE）理论采用的事实是，自由能的变化可以写为适当的概率分布函数的宏观涨落的广泛的性质的矩生成函数。本文导出了外磁场或外电场中系统的自由能与零场时“瞬时”磁化强度或极化强度分布之间的关系。这些分布的物理数学条件进行了讨论，并为几个连续和离散的模型分布的相应的热力学，或“统计状态”，推导。这些统计状态中的一些对应于众所周知的描述，例如朗之万和布里渊模型。所有的统计状态已经测试了几个磁性和介电系统：反铁磁氯化锰，二维伊辛自旋模型，和模拟的扩展简单点电荷（SPC/E）的水在电场下。结果表明，磁化强度和极化强度的离散建模对所有系统都是非常必要的。对于伊辛模型，“离散均匀”状态（对应于布里渊函数）给出了最好的描述。MnCl 2最好用“对称化二项式态”来描述，它反映了两个相反的磁性亚晶格。对于模拟的水，它被发现的偏振，以及类型的分布的波动，是强烈的影响系统的形状。(C)2002年美国物理学会。
The quasi-Gaussian entropy (QGE) theory employs the fact that a free-energy change can be written as the moment-generating function of the appropriate probability distribution function of macroscopic fluctuations of an extensive property. In this article we derive the relation between the free energy of a system in an external magnetic or electric field and the distribution of the "instantaneous" magnetization or polarization at zero field. The physical-mathematical conditions of these distributions are discussed, and for several continuous and discrete model distributions the corresponding thermodynamics, or "statistical state," is derived. Some of these statistical states correspond to well-known descriptions, such as the Langevin and Brillouin models. All statistical states have been tested on several magnetic and dielectric systems: antiferromagnetic MnCl2, the two-dimensional Ising spin model, and the simulated extended simple point charge (SPC/E) water under an electric field. The results indicate that discrete modeling of magnetization and polarization is rather essential for all systems. For the Ising model the "discrete uniform" state (corresponding to a Brillouin function) gives the best description. MnCl2 is best described by a "symmetrized binomial state," which reflects the two opposing magnetic sublattices. For simulated water it is found that the polarization, as well as the type of distribution of the fluctuations, is strongly affected by the shape of the system. (C) 2002 American Institute of Physics.