摘要
由于手征有效场论核力、量子多体关联方法和超级计算机能力的发展,原子核第一性原理计算或称从头计算(ab initio,first principles)在最近20年取得了巨大的进步.作为处理强关联多体问题的新秀,介质相似重整化群理论(in-medium similarity renormalization group,IMSRG)已经在原子核第一性原理计算中发挥了重要作用.虽然理论本身仍需进一步发展,但目前的计算已经可以达到较重核区,如已经成功地实现了对208Pb的收敛计算.本文简要回顾介质相似重整化群理论的发展历史,介绍我们在介质相似重整化群理论方面的最新发展,即复动量空间介质相似重整化群和形变介质相似重整化群.复空间介质相似重整化群方法包含了连续谱耦合作用,可以描述原子核的非束缚共振态和弱束缚特性.形变相似重整化群可以更有效地描述形变原子核的结构.
Over the past decades,ab initio nuclear calculations have made dramatic progress,especially reaching the heavy mass region as ^(208)Pb recently.These advances are driven by the concomitance of different factors.First,the chiral effective field theory (EFT) provides an efficient expansion and consistent treatment of both nuclear forces and electroweak currents.Second,renormalization methods for the nucleon-nucleon potential,in particular similarity renormalization group (SRG)significantly improves the convergence of numerical calculations with respect to basis truncations.Third,novel developments of accurate and uncertainty-controlled quantum many-body methods were carried out.Finally,the availability of high-performance computing resources has tremendously been increasing.As one of the powerful renormalization methods,the SRG has been applied to soften nuclear forces for ab initio calculations.Recently,the SRG method was developed as a novel many-body method in configuration space,named inmedium SRG (IMSRG).Since then,the IMSRG has been further developed,which includes multi-reference IMSRG,valence-space IMSRG,equation-of-motion IMSRG and IMSRG merging no-core shell model.The IMSRG has become one of the powerful and predictive ab initio methods.However,neither of these IMSRG variants can describe weaklybound nuclei due to the use of the harmonic oscillator (HO) basis.Moreover,open-shell nuclei with strong intrinsic deformation or shape coexistence remain a challenge due to the strong static correlations.The present paper summarizes the development history of the SRG and reviews our recent work on two IMSRG variants,named the Gamow IMSRG (G-IMSRG) and the deformed IMSRG (D-IMSRG),to include effects from the continuum coupling and the deformation within ab initio approaches.Weakly-bound and unbound nuclei belong to the category of open quantum systems,hence the coupling to the continuum profoundly affects their behaviors.The complex-energy Berggren basis provides an elegant framework to treat bound,resonant,and nonresonant continuum states on an equal footing.In the Berggren representation,we developed the novel ab initio G-IMSRG method which can describe the resonance and nonresonant continuum properties of weakly bound and unbound nuclei.Starting from chiral EFT two-and three-nucleon interactions,the Borromean halo nucleus ^(22)C has been calculated by the G-IMSRG.The halo structure is well reproduced,and low-lying resonant states are predicted for the future experiments.To capture the strong collective correlations,we developed the ab intio D-IMSRG approach starting from an axially deformed Hartree-Fock (HF) meanfiled.Important deformed configurations are efficiently included in the deformed basis,which is more efficient for nuclei with strong intrinsic deformation or shape coexistence.The calculation under the axially deformed HF basis breaks the SU(2) rotational symmetry (particle positions and internal spin states) associated with angular momentum conservation.The broken rotation symmetry could be restored by angular momentum projection.Nevertheless,it remains a challenge for both theory and numerical computation.We estimate the contribution from the angular momentum projection by the energy gain from the projected HF.As a proof of concept,we calculated the deformed (2-alpha cluster) ^(8,10)Be using chiral EFTinteractions.The calculated D-IMSRG energies with the estimated projection corrections agree with the“exact”results from the no-core shell model,which demonstrated the capability of this new method.After validating the new D-IMSRG,we systematically investigate the ground-state energies and charge radii of even-even nuclei from light beryllium to medium-mass magnesium isotopes.
作者
胡柏山
袁琪
范思钦
孙中浩
许甫荣
Baishan Hu;Qi Yuan;Siqin Fan;Zhonghao Sun;Furong Xu(State Key Laboratory of Nuclear Physics and Technology,School of Physics,Peking University,Beijing 10087l,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2023年第9期1016-1025,共10页
Chinese Science Bulletin
基金
国家重点研发计划(2018YFA0404401)
国家自然科学基金(11835001,11921006,12035001)资助。
关键词
第一性原理
手征有效场论
核力
介质相似重整化群
连续谱耦合
形变
ab initio,chiral effective field theory
nuclear force
in-medium similarity renormalization group
continuum coupling
deformation
作者简介
联系人:许甫荣,E-mail:frxu@pku.edu.cn。
