从第一原理出发计算原子结构有多种理论方法，它们都是基于变分原理的，其关键是构建一组最适合描述真实物理体系的且适用于变分原理的准完备基。然后在此基组的基础上进行各种物理过程相关物理量的计算。比如光电离过程中光电离截面的计算。光电离过程与天体物理、等离子物理、空间和大气物理等很多物理领域相关。光电离截面是这些领域中不可或缺的参数。近些年，随着激光冷却和囚禁原子技术的进步，对于激发态的光电离截面的研究越来越多。相对于实验测量的工作，激发态光电离截面的理论计算工作还比较少。本文中我们详细介绍了如何利用基于MCDF方法的全相对论计算程序GraspVU构建原子的准完备基。然后进行组态相互作用计算以充分考虑关联作用，并考虑电磁相互作用的延迟效应和量子电动力学等修正。该准完备基对原子结构和电磁跃迁等物理量可进行精密的理论计算。He体系的能级和跃迁速率等物理量的计算值与目前最准确的理论计算值以及精密的实验测量值符合很好。我们同时阐明了He等电子系列（Z≤36）1s2p 3P_0,1,2精细结构变化的机制：它是自旋-轨道相互作用和代表相对论延迟效应的Breit相互作用竞争的结果。同时该方案也适用于其它任何多电子原子体系；对Mg进行了精密理论计算，阐明了其3 3D、4 3D精细结构次序变化是自旋-轨道相互作用、关联作用、Breit作用、交换作用的相对论校正这四种相互抵消的机制竞争的结果。我们在MOT中测量了Rb原子5p3/2激发态的光电离截面，并用Breit-Pauli $R$-矩阵程序计算了Rb原子的基态以及激发态的光电离截面。在计算中，我们采用了构建原子准完备基的方案。我们的结果与其它理论和实验结果在误差范围内符合。构建原子准完备基的方案以及和$R$-矩阵方法的结合，预期能为等离子物理、天体物理、空间和大气物理等领域的研究提供大量精密的原子物理参数。精密的原子测量必须考虑到外场对能级的影响。光与原子的相干作用产生的电磁感应透明（EIT）效应受到人们的普遍关注，由于EIT介质具有吸收降低，色散变化剧烈等特点，在理论和实验上得到了人们的广泛研究。我们在实验中测量了磁光阱中冷87Rb原子的吸收谱，并结合四能级三光场EIT效应的相关理论进行了解释。

With the development of calculation technologies, theoretical calculations have been playing important roles in atomic and molecular physics. Based on the variation principle, many methods have been developed in atomic structure calculations. A high quality complete basis set is essential to the calculation of atomic structures and related physical parameters. Such as photoionization cross sections in photoionization process. Photoionization processes play important roles in plasma physics, laser physics, atmospheric science and astrophysics. The photoionization cross sections are the indispensable parameters in the relative fields. Excited-state photoionization processesare important in plasma discharges, laser-guided plasmas. In recent years, with the development of laser cooling and trapping techniques, there has been an increased interest in the study of photoionization cross sections of excited states. We present how to construct quasi-complete basis sets by using the full-relativistic GRASPVU program package, which is based on the multi-configuration Dirac-Fock method. The relativistic configuration interaction calculations are carried out by using the quasi-complete basis sets to consider adequate correlations. The relativistic retardation effectof electromagnetic interactions and the quantum electron dynamic corrections are also included. Our calculation results of He agree well with other theoretical results and experimental results, which validates our calculation scenario is applicable.Our calculations are full relativistic, and can be extended to high $Z$ helium-like ions in which the relativistic effect is important. We elucidate the mechanism of the interesting fine-structure splittings for the 1s2p 3P0,1,2 states along the helium isoelectronic sequence(Z≤36), i.e. the competitions between the spin-orbit interactions and the Breit interactions which represent the relativistic retardation effect of electromagnetic interactions. Our scenario of constructing quasi-complete basis sets can be used in any many-electron atomic system. We calculated the energy levels of Mg and elucidated the mechanism of its interestingfine-structure splittings of3 3D and 4 3D levels. The alkali-metal atoms as quasi-one electron systems have been proven to be an important and interesting testing ground for theoretical descriptions of photoionization processes. Many experimental works have been done. There are few theoretical calculations for the excited-state photoionization cross sections. We measured the photoionization cross sections of 5p3/2 of Rb in MOT and calculated the photoionization cross sections of low-lying states of Rb by using R-matrix method. Our results agree with other experimental and theoretical results within the error bars.Note that, our scenario of constructing quasi-complete basis sets for atomic calculations can be applied in R-matrix calculations. In precision measurement, the iterations between fields and atoms must be considered. Coherent field interacting with the multi-level atoms can lead to quantum interferenee, which could make significative physical phenomenon. As the typical one, the electromagnetically inducedtransparency(EIT) effect has been of great interest for the unique optical properties, such as the high transmission, steep dispersion and, so on. The cold atom media has become the research focus in quantum optics and atomic physics due to its low Doppler-broaden effect and decoherent effect by the collision.The absorbtion spectroscopy of cold Rb87 in a magneto-optical trap are measured with a weak probe beam. The absorbtion reduction dip due to EIT effect are observed, and a theoretical description is given by a four-level and three-light system.