Department of Chemistry, University College London, London WC1H 0AH, UK.
J Phys Condens Matter. 2010 Apr 28;22(16):165402. doi: 10.1088/0953-8984/22/16/165402. Epub 2010 Mar 30.
In a recent study we have reported a new type of trial wavefunction symmetric under the exchange of particles, which is able to describe a supersolid phase. In this work, we use the diffusion Monte Carlo method and this model wavefunction to study the properties of solid (4)He in two- and quasi-two-dimensional geometries. In the purely two-dimensional (2D) case, we obtain results for the total ground-state energy and freezing and melting densities which are in good agreement with previous exact Monte Carlo calculations performed with a slightly different interatomic potential model. We calculate the value of the zero-temperature superfluid fraction ρ(s)/ρ of 2D solid (4)He and find that it is negligible in all the considered cases, similarly to what is obtained in the perfect (free of defects) three-dimensional crystal using the same computational approach. Interestingly, by allowing the atoms to move locally in the direction perpendicular to the plane where they are confined to zero-point oscillations (quasi-2D crystal), we observe the emergence of a finite superfluid density that coexists with the periodicity of the system.
在最近的一项研究中，我们报告了一种新的粒子交换对称的试探波函数，它能够描述超固态相。在这项工作中，我们使用扩散蒙特卡罗方法和这个模型波函数来研究二维和准二维几何中固体 (4)He 的性质。在纯粹的二维 (2D) 情况下，我们得到了总基态能量以及冻结和熔化密度的结果，这些结果与以前使用略有不同的原子间势能模型进行的精确蒙特卡罗计算非常吻合。我们计算了 2D 固体 (4)He 的零温超流部分 ρ(s)/ρ 的值，并发现它在所有考虑的情况下都是微不足道的，这与使用相同计算方法的完美（无缺陷）三维晶体中得到的结果相同。有趣的是，通过允许原子在它们被限制在零动能振荡的平面的垂直方向上局部移动（准二维晶体），我们观察到有限的超流密度的出现，它与系统的周期性共存。
