铍和镁等电子序列的三阶多体微扰理论计算
Third-order many-body perturbation theory calculations for the beryllium and magnesium isoelectronic sequences
摘要：
在非虚对近似下，利用相对论三阶MBPT方法计算了具有两个价电子的离子的能量。302个三阶Goldstone图被组织成12个单体项和23个二体项。由于单体项与先前研究的单价离子中的三阶项相同，这里只给出三阶二体项和图。图的主导类被确定。模型势为Dirac-Hartree-Fock $V^{N-2}$势，数值计算中采用有限半径空腔中的B样条基函数。通过二阶微扰理论考虑了Breit相互作用，并计算了最低阶Lamb位移。对Z = 4- 7的类铍离子和类镁离子PIV进行了计算。三阶能量与测量结果非常吻合，对于所考虑的情况，精度为0.2%。与以前的二阶MBPT结果和其他计算进行比较。三阶能量校正是显着的，提高了一个数量级的二阶相关能量。
英文摘要：
Relativistic third-order MBPT is applied to obtain energies of ions with two valence electrons in the no virtual-pair approximation (NVPA). A total of 302 third-order Goldstone diagrams are organized into 12 one-body and 23 two-body terms. Only third-order two-body terms and diagrams are presented here, owing to the fact that the one-body terms are identical to the previously studied third-order terms in monovalent ions. Dominant classes of diagrams are identified. The model potential is a Dirac-Hartree-Fock $V^{N-2}$ potential, and B-spline basis functions in a cavity of finite radius are employed in the numerical calculations. The Breit interaction is taken into account through second order of perturbation theory and the lowest-order Lamb shift is also evaluated. Sample calculations are performed for berylliumlike ions with Z = 4--7, and for the magnesiumlike ion P IV. The third-order energies are in excellent agreement with measurement with an accuracy at 0.2% level for the cases considered. Comparisons are made with previous second-order MBPT results and with other calculations. The third-order energy correction is shown to be significant, improving second-order correlation energies by an order of magnitude.
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