高电荷态离子（HCI）光钟跃迁频率不确定度理论预期可低至E-19，将为原子时频标准提供新的频率参考跃迁，在更高精度水平上测量基本物理量、探索物理常数变化和验证基本物理定律。然而，由于数据缺乏和实验困难，目前还没有一种高电荷态离子被光频标实验所采纳。本项目拟围绕更高精度光频标的发展目标，开展相对论多体原子结构理论研究与计算，精确预言HCI能级和外场响应性质，寻找能级结构简单、自然线宽低于亚赫兹、对外场扰动不敏感、可实现多个离子同时探寻和主动激光的HCI光学跃迁，遴选适合光钟研制的HCI优选体系。我们已经开展了多个HCI等电子序列能级结构的相对论耦合簇计算，提出了四个新的HCI光钟候选离子，具有能级简单、钟跃迁线宽为亚赫兹、有冷却线和频率不确定度预期优于E-19的特点，具备了一定研究基础。本项目将为HCI光钟研制找到性质优越、技术可行性高的光频参考跃迁，并提供光谱和不确定度评估的高精度数据。

Optical clock transitions in highly charged ions (HCIs) are of lower fractional frequency uncertainty down to E-19 and has shown great potentials for precision measurement of fundamental physical constants, exploration of possible variation of physical constants, and test of basic physical theory at higher precision levels. However, as limited by scarcity of theoretical data and difficulty in experiments, none of the previously proposed highly charged ions is adopted in optical clocks so far. In this proposal, aiming to atomic frequency standard with higher precision, we are designed to develop high accuracy many-body theories and numerical methods of atomic structures to predict precise data of energy and properties of optical transitions, evaluate various systematical uncertainty due to external perturbations, and search promising HCI optical clock candidates that have simple energy-level structure, narrow linewidth down to sub-Hz, low sensibility to external perturbation, and being adapting to simultaneous interrogation and active clock laser output of multiple ions in specially designed traps, etc. We are going to propose selected HCIs for future development of HCI optical clocks. We have carried out relativistic coupled cluster calculations of several HCI isoelectronic sequences and proposed four new selected HCIs, which have simple energy-level structure, linewidth around sub-Hz, cooling lines, and fractional frequency uncertainty being less than E-19. We are going to find HCI candidates having excellent energy properties and strong technical feasibility and provide the high-accuracy data of frequencies and systematical uncertainties due to external perturbations.