Self-attracting polymers in two dimensions with three low-temperature phases
Self-attracting polymers in two dimensions with three low-temperature phases
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DOI：
10.1088/1751-8121/aa57a6
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发表时间：
2015-10
期刊：
影响因子：
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通讯作者：
A. Bedini;A. Owczarek;T. Prellberg
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文献类型：
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作者：
A. Bedini;A. Owczarek;T. Prellberg
我们通过蒙特卡罗模拟研究了所谓的顶点相互作用的自我回避行走（VISAW）模型的正方形晶格上的概括。这些构型实际上不是自回避行走，而是受限的自回避路径（键回避路径），只要路径不穿过自身，这些路径可以访问晶格的一个位点两次：为了区分这些路径的子集，我们将这些构型称为凹槽。三种不同的相互作用被添加到配置：首先VISAW相互作用，这是与双重访问的网站，其次是最近的邻居相互作用，以相同的方式作为规范的相互作用自避免行走（ISAW），第三，刚度能量，以提高或降低弯曲的概率的配置。除了正常的高温阶段，我们发现三个低温阶段：（i）通常的无定形液滴状“球状”相，（ii）具有由对齐的长直段组成的主导构型的各向异性“β-片层”相，其已在半柔性最近邻ISAW模型中发现，以及（iii）最大致密相，其中路径的所有站点都与先前在交互自回避轨迹中观察到的双重访问站点（除了配置的边界的那些站点）相关联。我们利用能量参数和三个序参量的涨落构造了相图。β-折叠相和最大密度相在相空间中似乎并不相交，并且总是被延伸相或球状相分开。我们把注意力集中在扩展和最大密度阶段之间的过渡，因为这是在原来的VISAW模型的过渡。我们发现，考虑的路径长度有一个范围内的参数的过渡是一阶，否则是连续的。
We study via Monte Carlo simulation a generalisation of the so-called vertex interacting self-avoiding walk (VISAW) model on the square lattice. The configurations are actually not self-avoiding walks but rather restricted self-avoiding trails (bond avoiding paths) which may visit a site of the lattice twice provided the path does not cross itself: to distinguish this subset of trails we shall call these configurations grooves. Three distinct interactions are added to the configurations: firstly the VISAW interaction, which is associated with doubly visited sites, secondly a nearest neighbour interaction in the same fashion as the canonical interacting self-avoiding walk (ISAW) and thirdly, a stiffness energy to enhance or decrease the probability of bends in the configuration. In addition to the normal high temperature phase we find three low temperature phases: (i) the usual amorphous liquid drop-like ‘globular’ phase, (ii) an anisotropic ‘β-sheet’ phase with dominant configurations consisting of aligned long straight segments, which has been found in semi-flexible nearest neighbour ISAW models, and (iii) a maximally dense phase, where the all sites of the path are associated with doubly visited sites (except those of the boundary of the configuration), previously observed in interacting self-avoiding trails. We construct a phase diagram using the fluctuations of the energy parameters and three order parameters. The β-sheet and maximally dense phases do not seem to meet in the phase space and are always separated by either the extended or globular phases. We focus attention on the transition between the extended and maximally dense phases, as that is the transition in the original VISAW model. We find that for the path lengths considered there is a range of parameters where the transition is first order and it is otherwise continuous.