The charge density wave (CDW) instability, usually occurring in low-dimensional metals, has been a topic of interest for longtime. However, some very fundamental aspects of the mechanism remain unclear. Recently, a plethora of new CDW materials, a substantial fraction of which is two-dimensional or even three-dimensional, has been prepared and characterised as bulk and/or single-layers. As a result, the need for revisiting the primary mechanism of the instability, based on the electron–hole instability established more than 50 years ago for quasi-one-dimensional (quasi-1D) conductors, has clearly emerged. In this work, we consider a large number of CDW materials to revisit the main concepts used in understanding the CDW instability, and emphasise the key role of the momentum dependent electron–phonon coupling in linking electronic and structural degrees of freedom. We argue that for quasi-1D systems, earlier weak coupling theories work appropriately and the energy gain due to the CDW and the concomitant periodic lattice distortion (PLD) remains primarily due to a Fermi surface nesting mechanism. However, for materials with higher dimensionality, intermediate and strong coupling regimes are generally at work and the modification of the chemical bonding network by the PLD is at the heart of the instability. We emphasise the need for a microscopic approach blending condensed matter physics concepts and state-of-the-art first-principles calculations with quite fundamental chemical bonding ideas in understanding the CDW phenomenon in these materials.

中文翻译：

---

低维系统中电荷密度波的结构方法：电子不稳定性和化学键合


电荷密度波（CDW）不稳定性通常发生在低维金属中，长期以来一直是人们感兴趣的话题。然而，该机制的一些非常基本的方面仍不清楚。最近，大量新型 CDW 材料（其中很大一部分是二维甚至三维）已被制备并表征为块状和/或单层。因此，基于 50 多年前建立的准一维（准一维）导体的电子-空穴不稳定性，显然需要重新审视不稳定性的主要机制。在这项工作中，我们考虑了大量的 CDW 材料，重新审视用于理解 CDW 不稳定性的主要概念，并强调动量依赖的电子-声子耦合在连接电子和结构自由度中的关键作用。我们认为，对于准一维系统，早期的弱耦合理论适用，并且由于 CDW 和伴随的周期性晶格畸变 (PLD) 带来的能量增益仍然主要归因于费米表面嵌套机制。然而，对于更高维度的材料，中间和强耦合机制通常起作用，并且 PLD 对化学键网络的修改是不稳定的核心。我们强调需要一种微观方法，将凝聚态物理概念和最先进的第一原理计算与非常基本的化学键思想相结合，以理解这些材料中的 CDW 现象。