Ab initio modelling of structural and magnetic phase transitions under pressure and doping for the iron based superconductors

本项目的目标是通过从头算密度泛函理论（DFT）计算、Car- Parrinello分子动力学和动态平均场理论（DMFT）的结合，更好地理解铁基超导体中磁性、结构跃迁和超导性作为压力和掺杂的函数之间的相互作用。我们将探索这些多波段系统的结构、磁性和超导相变的本质i)通过在第一性原理（Car- Parrinello）分子动力学框架内进行电子结构计算。我们将比较波段结构与ARPES结果。Ii)在不同压力和掺杂下进行动量依赖和轨道分辨的磁化率计算。对于后者，我们将在DFT内实现相应矩阵元素的求值。这些计算将使我们能够量化带内和带间以及轨道内和轨道间嵌套的数量，这可能是理解磁性和超导性之间相互作用的关键数量。iii)对DFT和DMFT中压力和掺杂的光学特性进行系统的研究。将分析这些材料可能的相关性质。iv)通过计算与角度相关的德哈斯-范阿尔芬（dHvA）频率，并将其与现有测量结果进行比较。这些计算将允许更好地表征费米表面在压力和掺杂下的演变。V)从磁化率计算和非共线计算两方面分析了这些系统在压力下的自旋动力学。在硫族铁（“11”）化合物中，观察到非共线磁基态，需要通过相应的计算来解决。最后，我们计划在DFT中寻找适当的交换相关泛函，以便更好地预测结构和磁性能。

The goal of this project is a better understanding of the interplay between magnetism, structural transitions and superconductivity as a function of pressure and doping in the iron-based superconductors by a combination of ab initio density functional theory (DFT) calculations, Car- Parrinello molecular dynamics and dynamical mean field theory (DMFT). We will explore the nature of the structural, magnetic and superconducting phase transitions in these multiband systems i) by performing electronic structure calculations in the framework of first principles (Car- Parrinello) molecular dynamics. We will compare bandstructures with ARPES results. ii) by performing momentum-dependent and orbital-resolved susceptibility calculations at various pressures and dopings. For the latter we will implement the evaluation of the corresponding matrix elements within DFT. These calculations will allow us to quantify the amount of intra- and inter-band as well as intra- and inter-orbital nesting, which may be a key quantity for understanding the interplay between magnetism and superconductivity. iii) by performing a systematic investigation of the optical properties as a function of pressure and doping within DFT and DMFT. The possible correlated nature of these materials will be analyzed. iv) by calculating angle dependent de Haas-van Alphen (dHvA) frequencies and compare them to available measurements. These calculations will allow a better characterization of the evolution of Fermi surfaces under pressure and doping. v) by analyzing the spin dynamics in these systems under pressure in terms of susceptibility calculations as well as non-collinear calculations. In the iron chalcogenide (“11”) compounds, a non-collinear magnetic ground state was observed, which needs to be addressed by corresponding calculations. And finally we plan to search for adequate exchange-correlation functionals within DFT that allow a better prediction of structures and magnetic properties.