【作者】 杨刚；

【导师】 包括；

【作者基本信息】 吉林大学 ， 凝聚态物理， 2020， 硕士

【摘要】 氢是宇宙中最简单也是最丰富的元素,对它的研究一直是高压物理领域核心问题之一。在本论文中我们以氢分子为研究对象,应用椭球模型,来研究压力和压力与磁场联合作用对氢分子性质的影响。为了更真实的了解氢分子内部的行为,充分考虑了原子核的运动对氢分子行为的影响,使用了量子蒙特卡罗方法进行精确的数值模拟,发现了:1.由于我们充分考虑了原子核的运动,可以体现出原子核质量不同带来的影响,即同位素差异。经与前人固定原子核模型相比,我们的氢、氘模型在相同的摩尔密度下具有更高的总能和压力,并且具有更低的可压缩性和更复杂的几何变化规律,如键长,椭球的长、短轴等的变化;无论氢还是氘,它们的原子核的动能都在电子的千分之一量级,但是,原子核的运动会影响总能量,使其明显升高,尤其是在高压下这种影响更为显著;在相同的摩尔密度下,氢的总能和压力均高于氘的;我们发现一些物理量之间存在的数值关系,如分子的总能量与受限分子的椭球体积的倒数成线性关系,以及系统的压力与摩尔密度的平方成线性关系;氘和氢在键长压缩率,束缚椭球的拓扑性质等的压缩性质上存在很大差异,这可以解释它们相图存在差异的原因,以及氘独特的Ⅰ’、II’相。2.在有磁场的情况下,当在同等束缚体积的情况下,分子总能增高,体系总能量与体积倒数的正比关系可延续到更小的束缚体积;依旧存在压强与密度平方成正比的关系;在有磁场情况下,氢分子键长在同等压强下更短,这在较低压力下更为明显;在有磁场情况的同等束缚体积下,电子动能有所提高,在电子动能与体积倒数关系曲线上,明显能看到三个区域,而原子核动能呈现出与上述三个区域对应的台阶式变化;电子、原子核之间相互作用势能有所降低,在低压下尤为显著,而核间及电子之间的作用势能有所升高;对于椭球形状上的变化,有磁场与无磁场情况相似。以上研究为理解压力下氢不同同位素相图差异提供了帮助,为密度泛函等以绝热近似为基础的计算模拟进行修正,为了解强磁场下氢的状态等提供数据支撑。更多还原

【Abstract】 Hydrogen is the most abundant and simplest element in the universe,and its research has always been one of the core issues in the field of high-pressure physics.In this thesis,we take hydrogen molecules as the research object,and use the ellipsoid model to study the effect of pressure and pressure joint with magnetic field on the properties of hydrogen molecules.In order to understand the internal behavior of the hydrogen molecule more realistically,the influence of the movement of the nucleus on the behavior of hydrogen molecule was fully considered,and the accurate simulation was carried out by using the Quantum Monte Carlo method.,we found:By fully considered the he movement of the atomic nucleus,it can reflect the influence brought by the difference in atomic nucleus quality,that is,the difference in isotopes.Compared with the predecessor fixed nuclear model,our hydrogen /deuterium model has higher total energy and pressure at the same molar density,and has lower compressibility and more complex geometric change law,such as bond length,the long axis / short axis of ellipsoid.Whether hydrogen or deuterium,the kinetic energy of their nuclei is in the order of one-thousandth of an electron,but the movement of the nuclei affects the total energy,especially under high pressure.At the same molar density,the total energy and pressure of hydrogen are higher than those of deuterium.We found that there are numerical relationships between some physical quantities,such as the linear relationship between the total energy of a molecule and the reciprocal of the volume of the ellipsoid of the confined molecule,and the linearrelationship between the pressure of the system and the square of the number of moles of density.Deuterium and hydrogen have great differences in compressive properties such as bond length compressibility,topological properties of bound ellipsoid,etc.,which may explain the difference in their phase diagrams and the unique Ⅰ’ and II’phases of deuterium.In the presence of a magnetic field,the total molecular energy is higher than when there is no magnetic field under the same bound volume,and the proportional relationship between the total energy of the system and the reciprocal of the volume can continue to a smaller bound volume;There is still a proportional relationship between the pressure and the square of the density;In the presence of a magnetic field,the hydrogen molecular bond length is shorter at the same pressure,which is more obvious at lower pressures;In the case of magnetic field,the electron kinetic energy is improved in the case of the same bound volume.On the curve of the relationship between the electron kinetic energy and the reciprocal volume,three regions can be clearly seen,the nuclear kinetic energy shows a stepped change corresponding to the three regions.The interaction potential energy between electron and nucleus decreases,especially at low pressure,while the interaction potential energy between nuclei and between electrons increases.In the shape change of ellipsoid,magnetic field is similar to that in the absence of magnetic field.The above research provides help to understand the difference in phase diagrams of different hydrogen isotopes under pressure,corrects calculations based on adiabatic approximation such as density functional,and provides data support for understanding the state of hydrogen under strong magnetic fields.更多还原