The application of a temperature gradient to an extended system generates an electromotive force that induces an electric current in conductors and a macroscopic polarization in insulators. The ratio of the electromotive force to the temperature difference, usually referred to as the Seebeck coefficient, is often computed using non-equilibrium techniques, such as non-equilibrium molecular dynamics (NEMD). In this paper we argue that thermo-polarization effects in insulating fluids can be conveniently treated by standard equilibrium thermodynamics and devise a protocol, based on a combination of equilibrium molecular dynamics and Bayesian inference methods, that allows one to compute the Seebeck coefficient in these systems along with a rigorous estimate of the resulting statistical accuracy. The application of our methodology to liquid SPC/E water results in good agreement with previous studies, based on more elaborate NEMD simulations, and in a more reliable estimate of the statistical accuracy of the results.
自旋塞贝克效应(SSE),即由热产生自旋电流,已经在各种磁性材料中得到了广泛的研究,包括铁磁体、反铁磁体、顺磁体和量子自旋液体。本文报道了具有准一维自旋1/2链的自旋能隙量子磁体候选物Pb_2V_3O_9单晶中的SSE的研究。详细的温度和磁场依赖性的SSE的调查,和温度依赖的临界磁场显示出很强的相关性的玻色-爱因斯坦凝聚相的量子磁体Pb 2 V3 O 9。这一工作显示了利用自旋流作为探针研究量子磁体中自旋关联和相变性质的潜力。
Experimentally Probing the Libration of Interfacial Water: the Rotational Potential of Water is Stiffer at the Air/Water Interface than in Bulk Liquid
液态水的大多数性质是由它的氢键网络决定的。因为形成水界面需要终止该网络,所以人们可能期望界面水的分子水平性质与本体水显著不同。有趣的是,许多先前的实验和理论工作已经发现,从它们的时间平均结构和皮秒结构动力学的角度来看,在空气/水界面处的氢键结合的OH基团与在大量液态水中的氢键结合的OH基团的行为相同。在这里,我们报告的第一个实验观察界面水的天平动(即受抑旋转)使用基于激光的技术振动和频光谱。我们发现这种模式的频率为834 cm $^{-1}$,比相同温度下的散装液态水高$\approx 165$ cm $^{-1}$,与散装冰相似。由于振动频率与水的旋转势的刚度成比例,因此这种增加表明在空气/水界面处终止本体水的氢键网络的一个效果是阻碍水围绕完整的氢键的旋转。由于在散装液态水的天平动起着关键作用,在稳定反应中间体和耗散多余的振动能量,我们希望能够探测这种模式在界面水在水界面的非均相反应的动力学打开新的视角。
Structural, Electronic, and Dynamical Properties of Liquid Water by ab initio Molecular Dynamics based on SCAN Functional within the Canonical Ensemble
采用SCAN元-GGA泛函近似,对正则系综中的液态水进行了从头算分子动力学(AIMD)模拟,并与GGA水平的PBE泛函和包含PBE泛函的Tkatchenko-Scheffler van der Waals(vdW)色散修正的结果进行了系统的比较.我们分析了液态水的各种性质,包括径向分布函数,氧-氧-氧三重态角分布,四面体,氢键,扩散系数,环统计,态密度,带隙和偶极矩。我们发现,扫描功能通常是更准确的比其他两个功能的液态水,不仅捕获的中程VDW相互作用,但也减轻了PBE模拟中规定的过于强大的氢键。我们还比较了基于扫描的AIMD模拟的结果在典型的等温等压合奏。我们的研究结果表明,SCAN提供了一个可靠的描述大多数结构,电子和动力学性质的液态水。
Bond orientational ordering in liquids: Towards a unified description of water-like anomalies, liquid-liquid transition, glass transition, and crystallization