Abstract

We discuss a two-dimensional model that leads to a phase diagram which reproduces at least qualitatively that of a pure substance. It is known that a spring between two atoms is due to a bond created by the interaction between the electrons of both atoms. Consequently a variation of the quantum state of the electrons involved in the bond can modify the elastic force constant of the spring. That is a kind of atom-phonon coupling. We consider a square lattice of N identical atoms linked by springs between atoms first and second nearest neighbors. We assume that the elastic force constants of all the springs can vary. The system is studied by using a variational method. First order phase transitions are obtained. The phase diagram of the system displays the features observed in the phase diagram of a pure substance: three thermodynamic phases, three coexistence curves, one triple point and one critical point. Applied pressure can be introduced in the model.

Graphical abstract

中文翻译：

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纯物质的相图？

摘要

我们讨论了一个二维模型，该模型导致了一个相图，该相图至少定性地再现了纯物质的相图。众所周知，两个原子之间的弹簧是由于两个原子的电子之间的相互作用所产生的键。因此，键中所涉及的电子的量子态的变化可以改变弹簧的弹力常数。那是一种原子-声子耦合。我们考虑N的方格相同的原子通过弹簧连接在第一和第二近邻之间。我们假设所有弹簧的弹力常数可以变化。通过使用变分方法来研究该系统。获得一阶相变。该系统的相图显示了在纯物质相图中观察到的特征：三个热力学相，三个共存曲线，一个三点和一个临界点。可以在模型中引入施加的压力。

图形概要