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arXiv 1004.4378cond-mat.mtrl-scicond-mat.stat-mech
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二维晶体热力学稳定性的扩展耦合格式

The Thermodynamic Stability of Two Dimensional Crystals with an Extended Coupling Scheme

D. J. Priour

摘要:

我们计算均方差晶体在一个和两个维度。对于二维晶格,我们考虑了几种不同的几何形状(即正方形,三角形和蜂窝),我们发现相同的基本现象,为每个晶格结构。我们研究了各种耦合方案下长程晶序的稳定性,包括短程指数衰减的原子间势和具有幂律依赖性r^{-alpha}的长程相互作用。对于后者在一维情况下,我们发现一个临界值α_c(1D)= 1.615 +/- 0.005的幂律衰减指数低于该值时,晶体有序是完整的,高于该值时,当T > 0时,热涨落破坏了长程序。对于位移局限于平面的二维晶格,相应的临界值为α_c(2D)= 3.15 +/ 0.025。如果允许垂直于晶面的运动,则热致变形在具有由扩展耦合方案提供的局部刚度的双层系统中迅速地(即线性地)发散,即使相互作用是长程的,在晶格位点之间的分离中作为幂律衰减。

英文摘要:

We calculate mean square deviations for crystals in one and two dimensions. For the two dimensional lattices, we consider several distinct geometries (i.e. square, triangular, and honeycomb), and we find the same essential phenomena for each lattice structure. We investigate the stability of long-range crystalline order for a variety of coupling schemes, including short-range exponentially decaying inter-atomic potentials and long-range interactions with a power law dependence r^{-alpha}. For the latter in the 1D case, we find a critical value alpha_c(1D) = 1.615 +/- 0.005 for the power law decay exponent below which crystalline order is intact, and above which thermal fluctuations destroy long-range order when T > 0. The corresponding critical value for two dimensional lattices with displacements confined to the plane is alpha_c(2D) = 3.15 +/ 0.025. If motion perpendicular to the crystal plane is permitted, thermally induced distortions diverge rapidly (i.e. linearly) in dual layer systems with local stiffness provided by an extended coupling scheme, even if the interaction is long ranged, decaying as a power law in the separation between lattice sites.

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