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1. Bound and autoionizing potential energy curves in the CH molecule

   https://doi.org/10.1063/5.0177822  

   Hvizdoš, Dávid; Forer, Joshua; Kokoouline, Viatcheslav; Greene, Chris H (December 2023, The Journal of Chemical Physics)

   This article presents a method of computing bound state potential curves and autoionizing curves using fixed-nuclei R-matrix data extracted from the Quantemol-N software suite. It is a method based on two related multichannel quantum-defect theory approaches. One is applying bound-state boundary conditions to closed-channel asymptotic solution matrices, and the other is searching for resonance positions via eigenphase shift analysis. We apply the method to the CH molecule to produce dense potential-curve datasets presented as graphs and supplied as tables in the publication supplement. 

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2. Deep Just-in-Time Defect Prediction: How Far Are We?

   https://doi.org/10.1145/3460319.3464819  

   Zeng, Zhengran; Zhang, Yuqun; Zhang, Haotian; Zhang, Lingming (July 2021, ACM SIGSOFT International Symposium on Software Testing and Analysis)

   Defect prediction aims to automatically identify potential defective code with minimal human intervention and has been widely studied in the literature. Just-in-Time (JIT) defect prediction focuses on program changes rather than whole programs, and has been widely adopted in continuous testing. CC2Vec, state-of-the-art JIT defect prediction tool, first constructs a hierarchical attention network (HAN) to learn distributed vector representations of both code additions and deletions, and then concatenates them with two other embedding vectors representing commit messages and overall code changes extracted by the existing DeepJIT approach to train a model for predicting whether a given commit is defective. Although CC2Vec has been shown to be the state of the art for JIT defect prediction, it was only evaluated on a limited dataset and not compared with all representative baselines. Therefore, to further investigate the efficacy and limitations of CC2Vec, this paper performs an extensive study of CC2Vec on a large-scale dataset with over 310,370 changes (8.3 X larger than the original CC2Vec dataset). More specifically, we also empirically compare CC2Vec against DeepJIT and representative traditional JIT defect prediction techniques. The experimental results show that CC2Vec cannot consistently outperform DeepJIT, and neither of them can consistently outperform traditional JIT defect prediction. We also investigate the impact of individual traditional defect prediction features and find that the added-line-number feature outperforms other traditional features. Inspired by this finding, we construct a simplistic JIT defect prediction approach which simply adopts the added-line- number feature with the logistic regression classifier. Surprisingly, such a simplistic approach can outperform CC2Vec and DeepJIT in defect prediction, and can be 81k X/120k X faster in training/testing. Furthermore, the paper also provides various practical guidelines for advancing JIT defect prediction in the near future. 

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3. The quest to uncover the nature of benzonitrile anion

   https://doi.org/10.1039/C9CP06484B  

   Gulania, Sahil; Jagau, Thomas-C.; Sanov, Andrei; Krylov, Anna I. (March 2020, Physical Chemistry Chemical Physics)

   Anionic states of benzonitrile are investigated by high-level electronic structure methods. The calculations using equation-of-motion coupled-cluster theory for electron-attached states confirm earlier conclusions drawn from the photodetachment experiments wherein the ground state of the anion is the valence 2 B 1 state, while the dipole bound state lies adiabatically ∼0.1 eV above. Inclusion of triple excitations and zero-point vibrational energies is important for recovering relative state correct ordering. The computed Franck–Condon factors and photodetachment cross-sections further confirm that the observed photodetachment spectrum originates from the valence anion. The valence anion is electronically bound at its equilibrium geometry, but it is metastable at the equilibrium geometry of the neutral. The dipole-bound state, which is the only bound anionic state at the neutral equilibrium geometry, may serve as a gateway state for capturing the electron. Thus, the emerging mechanistic picture entails electron capture via a dipole bound state, followed by non-adiabatic relaxation forming valence anions. 

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4. Excitations of quantum Ising chain CoNb2O6 in low transverse field: Quantitative description of bound states stabilized by off-diagonal exchange and applied field

   https://doi.org/10.1103/PhysRevB.108.184417  

   Woodland, Leonie; Lovas, Izabella; Telling, M; Prabhakaran, D; Balents, Leon; Coldea, Radu (November 2023, Physical Review B)

   We present experimental and theoretical evidence of novel bound state formation in the low transverse field or- dered phase of the quasi-one-dimensional Ising-like material CoNb2O6. High-resolution single-crystal inelastic neutron scattering measurements observe that small transverse fields lead to a breakup of the spectrum into three parts, each evolving very differently upon increasing field. This can be naturally understood starting from the excitations of the ordered phase of the transverse field Ising model, domain wall quasiparticles (solitons). Here, the transverse field and a staggered off-diagonal exchange create one-soliton hopping terms with opposite signs. We show that this leads to a rich spectrum and a special field, when the strengths of the off-diagonal exchange and transverse field match, at which solitons become localized; the highest field investigated is very close to this special regime. We solve this case analytically and find three two-soliton continua, along with three novel bound states. Perturbing away from this novel localized limit, we find very good qualitative agreement with the experimental data. We also present calculations using exact diagonalization of a recently refined Hamiltonian model for CoNb2O6 and using diagonalization of the two-soliton subspace, both of which provide a quantitative agreement with the observed spectrum. The theoretical models qualitatively and quantitatively capture a variety of nontrivial features in the observed spectrum, providing insight into the underlying physics of bound state formation. 

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5. Exact symmetries and threshold states in two-dimensional models for QCD

   https://doi.org/10.1007/JHEP10(2021)096  

   Dempsey, Ross; Klebanov, Igor R.; Pufu, Silviu S. (October 2021, Journal of High Energy Physics)

   null (Ed.)

   A bstract Two-dimensional SU( N ) gauge theory coupled to a Majorana fermion in the adjoint representation is a nice toy model for higher-dimensional gauge dynamics. It possesses a multitude of “gluinoball” bound states whose spectrum has been studied using numerical diagonalizations of the light-cone Hamiltonian. We extend this model by coupling it to N f flavors of fundamental Dirac fermions (quarks). The extended model also contains meson-like bound states, both bosonic and fermionic, which in the large- N limit decouple from the gluinoballs. We study the large- N meson spectrum using the Discretized Light-Cone Quantization (DLCQ). When all the fermions are massless, we exhibit an exact $$ \mathfrak{osp} $$ osp (1|4) symmetry algebra that leads to an infinite number of degeneracies in the DLCQ approach. More generally, we show that many single-trace states in the theory are threshold bound states that are degenerate with multi-trace states. These exact degeneracies can be explained using the Kac-Moody algebra of the SU( N ) current. We also present strong numerical evidence that additional threshold states appear in the continuum limit. Finally, we make the quarks massive while keeping the adjoint fermion massless. In this case too, we observe some exact degeneracies that show that the spectrum of mesons becomes continuous above a certain threshold. This demonstrates quantitatively that the fundamental string tension vanishes in the massless adjoint QCD 2 without explicit four-fermion operators. 

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