The no-core shell model (NCSM) is an \textit{ab initio} method that solves the nuclear many-body problem by expanding the many-particle wave function into a (typically) harmonic oscillator basis and minimizing the energy to obtain the expansion coefficients. Extensions of the NCSM, such as its coupling with microscopic-cluster basis states, further allow for an \textit{ab initio} treatment of light-ion nuclear reactions of interest for both astrophysics and nuclear technology applications. A downside of the method is the exponential scaling of the basis size with increasing number of nucleons and excitation quanta, which limits its applicability to mass $A\lesssim 16$ nuclei, except for variants where the basis is further down-selected via some truncation scheme. We consider a basis selection method for the NCSM that captures the essential degrees of freedom of the nuclear wave function leading to a favorable complexity scaling for calculations and enabling \textit{ab initio} reaction calculations in $sd$-shell nuclei. The particle configurations within the NCSM basis are ordered based on their contribution to the first moment of the Hamiltonian matrix that results from the projection onto the many-body basis. The truncation scheme then consists in retaining only the lowest-first-moment configurations, which typically contain only few many-body basis states (Slater determinants). We present calculations for $^7$Li and $n+^{12}$C scattering using nucleon-nucleon interactions derived from chiral effective field theory and softened using the similarity renormalization group method. The obtained energy levels invariably demonstrate exponential convergence with the size of the basis, and we find improved convergence in scattering calculations. To demonstrate the possibilities enabled by the approach, we also present a first calculation for the scattering of neutrons from $^{24}$Mg.
$\boldsymbol{\textit{Ab initio}}$ $nα$ scattering using the Efros method
Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；College of Physics and Engineering, Henan University of Science and Technology（河南科技大学物理与工程学院）；State Key Laboratory of Heavy Ion Science and Technology, Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所重离子科学和技术国家重点实验室）；Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University（莫斯科国立大学索别利茨基核物理研究所）；Department of Physics and Astronomy, Iowa State University（爱荷华州立大学物理与天文系）
Toward $\textit{Ab Initio}$ Quantum Simulations of Atomic Nuclei Using Noisy Qubits
State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University（北京大学物理学院核物理与技术国家重点实验室）；Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所南方核科学理论中心）
First \textit{ab initio} calculations of first-forbidden $β$ transitions in the reactor antineutrino anomaly
Peking University（北京大学）；School of Physics, and State Key Laboratory of Nuclear Physics and Technology, Peking University（北京大学物理学院，核物理与技术国家重点实验室）；Institute of Modern Physics, Fudan University（复旦大学现代物理研究所）；Shanghai Research Center for Theoretical Nuclear Physics, NSFC and Fudan University（上海理论核物理研究中心，NSFC和复旦大学）；Southern Center for Nuclear-Science Theory, Institute of Modern Physics, Chinese Academy of Sciences（中国科学院现代物理研究所南方核科学理论中心）
$^6$He structure from semiclassical 3D models based on $\textit{ab initio}$ spatial correlations
Iowa State University（爱荷华州立大学）；Instituto Tecnológico de Aeronáutica（航空技术学院）；Henan University of Science and Technology（河南科技大学）；Chinese Academy of Sciences（中国科学院）
\textit{Ab initio} study of spectroscopic factors in $^{48}$K and neighboring $N=28$ isotones
Advanced Energy Science and Technology Guangdong Laboratory（广东先进能源科学与技术实验室）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；Heavy Ion Science and Technology Key Laboratory（重离子科学与技术重点实验室）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学技术大学核科学与技术学院）；Southern Center for Nuclear-Science Theory (SCNT)（南方核科学理论中心）
Halo structure of $^6$He from $\textit{ab initio}$ two-nucleon spatial correlations
Iowa State University（爱荷华州立大学）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Instituto Tecnológico de Aeronáutica（航空技术学院）；Henan University of Science and Technology（河南科技大学）；Chinese Academy of Sciences（中国科学院）
Full Configuration Interaction Quantum Monte Carlo for Accurate $\textit{Ab Initio}$ Nuclear Structure Calculations
School of Physics, and State Key Laboratory of Nuclear Physics and Technology, Peking University（北京大学物理学院，核物理与技术国家重点实验室）；Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所，南方核科学理论中心）；Max Planck Institute for Solid State Research（马克斯·普朗克固体研究所）；Department of Chemistry, University of Cambridge（剑桥大学化学系）
Ab initio charge form factors and radii of light isoscalar nuclei: Role of the two-body charge density
Forschungszentrum Jülich（于利希研究中心）；Ruhr-Universität Bochum（波鸿鲁尔大学）；Universität Bonn（波恩大学）；Helmholtz-Institut für Strahlen- und Kernphysik（亥姆霍兹射线与核物理研究所）；Bethe Center for Theoretical Physics（贝特理论物理中心）；Peng Huanwu Collaborative Center for Research and Education, International Institute for Interdisciplinary and Frontiers, Beihang University（北京航空航天大学国际交叉前沿研究院彭桓武教研协同中心）
Full configuration interaction quantum Monte Carlo for accurate $\textit{ab initio}$ nuclear structure calculations: algorithms and calculation details
School of Physics, and State Key Laboratory of Nuclear Physics and Technology, Peking University（北京大学物理学院，核物理与技术国家重点实验室）；Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所南方核科学理论中心(SCNT)）；Max Planck Institute for Solid State Research（马克斯·普朗克固体研究所）；Department of Chemistry, University of Cambridge（剑桥大学化学系）
Chiral three-nucleon forces for the new local position-space two-nucleon potential in $\textit{ab initio}$ many-body calculations
School of Physics, and State Key Laboratory of Nuclear Physics and Technology, Peking University（北京大学物理学院及核物理与核技术国家重点实验室）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所南方核科学理论中心）
