About

Chenchen Song is an Assistant Professor of Chemistry at UC Davis, appointed in 2021. His research focuses on theoretical chemistry, specifically on developing quantum chemistry and excited state dynamics methods from first principles to understand photochemical processes and their practical applications. His work combines quantum chemistry methods with advances in computer science, such as specialized hardware like graphical processing units (GPUs), and mathematical techniques like tensor factorizations. His research interests include applying these theoretical tools to photochemistry in biological systems, such as bioluminescence and visual processes, as well as renewable energy applications like light harvesting complexes. Dr. Song earned his Ph.D. in Chemistry from Stanford University in 2018, following his B.S. in Chemistry from Tsinghua University in 2012. He completed postdoctoral fellowships at the University of California, Berkeley, and Lawrence Berkeley National Lab from 2018 to 2021 before joining UC Davis. His contributions include developing new physical insights into computational methods such as XMS-CASPT2, state-averaged CASSCF, and polarizable models for simulating photoreactions in proteins and solvents. His work aims to provide a deeper understanding of photochemical processes through innovative theoretical approaches.

Research topics

• Computer Science
• Physics
• Chemistry
• Quantum mechanics
• Computational science
• Computational chemistry
• Computer graphics (images)
• Physical chemistry
• Parallel computing
• Mathematics
• Atomic physics
• Geometry

Selected publications

• Mechanical Property Enhancement Mechanism of W/TC4 Composites by Laser‐Directed Energy Deposition

  Advanced Engineering Materials · 2026-03-17

  article

  Titanium‐based composites represent one of the key development directions for new materials in aerospace applications. In this article W/TC4 composites with high W addition (wt%) were prepared by laser‐directed energy deposition technology. The melting of W particles and the precipitation process of W dendrites were revealed. The mechanism of W addition on microstructure refinement and mechanical properties improvement of composites was described. The results indicate that W particles form a strong metallurgical bond with the Ti alloy matrix, and dendritic or granular substitution solid solutions composed of W and Ti have appeared within the Ti alloy matrix. The addition of W exhibits a pronounced effect on grain refinement. In composite specimens containing 70 wt% W, the average grain size of β‐Ti reached 14.34 μm, which is over 40% smaller than that observed in specimens with 50 wt% W. Furthermore, the anisotropy of the composite material significantly decreased with increasing W content. As the W content increases, the microhardness of the composite material gradually rises. Among them, the microhardness of the W 70 wt% specimen reached 472.9 ± 29.7 HV 0.2 . The increase in microhardness is primarily attributed to the load‐bearing strengthening effect of unmelted W particles and the solid solution strengthening effect of the W element. Furthermore, friction and wear tests indicate that both the arithmetic average height and mean square height of the wear surface gradually increase with the rising proportion of W addition.

  PublisherDOI

• Molecular conical intersections with odd electron number are realizations of the topological Yang monopole

  The Journal of Chemical Physics · 2026-02-27

  article1st authorCorresponding

  The two-level conical intersection of a molecule with an odd electron number in the absence of a magnetic field obeys time-reversal symmetry T2 = -1 (referred to as the T2 = -1 conical intersection) and has a five-dimensional branching space due to the Kramer degeneracy. Similar to how the conical intersection of a molecule in a magnetic field (T2 = 0) behaves as the Dirac monopole, the T2 = -1 conical intersection behaves as the Yang monopole, a mathematical generalization of the Dirac monopole with SU(2) gauge field and SO(5) symmetry. This implies that we can study the topological properties of T2 = -1 conical intersections in chemistry based on what is known about the Yang monopole in high energy physics. In this work, we present a few mathematical tools to study this connection. First, we show that geometric algebra and quaternion numbers together provide a natural way to utilize the T2 = -1 time reversal symmetry and the SO(5) symmetry in scaled coordinates, making it simple to derive eigenfunctions, Berry connection, and Berry curvature of T2 = -1 conical intersection. In particular, this approach provides a simple proof that when viewed from the upper or lower states, the T2 = -1 conical intersection behaves as the self-dual or self-antidual Yang monopole with second Chern number C2=+122 or -122, respectively. In addition, we propose a visualization method for the SU(2) Berry connection of T2 = -1 conical intersection. This is achieved by showing that the non-zero part of the Berry connection induces a Hopf-fibration on the S3 longitude space, which is further visualized through stereographic projection.

  PublisherDOI

• Study on micromechanical mechanism of ionic environment affecting adsorption behavior between graphene and benzene

  Separation and Purification Technology · 2025-04-23 · 5 citations

  articleOpen access1st author

  As the ion concentration increased, the adsorption of benzene on graphene was initially slightly enhanced, but then significantly inhibited. At the same ion concentration, higher ionic valence was more favorable to adsorption than lower ionic valence. Comparative analysis demonstrated that ion concentration exerts a greater influence on the adsorption behavior than ionic valence. • Single-bond forces at different ion environment were obtained by AFM experiments. • Ions will change ESP charge and preempt adsorption sites on the graphene surface. • Ion concentration first promoted and then inhibited graphene adsorbing benzene. • Higher ion valence was more favorable to adsorption than lower ion valence. • The influence of ion concentration on adsorption is greater than that of ion valence. Graphene, an adsorbent material with excellent recyclability and large specific surface area, can effectively adsorb or desorb benzene-containing pollutant molecules in wastewater. In this study, we employed a combination of theoretical analysis, molecular dynamics simulations and atomic force microscopy experiments to elucidate the micromechanical mechanisms by which the ionic environment affects the π-π interactions between benzene and graphene. The results reveal that as the ion concentration increases, the adsorption behavior of graphene toward benzene rings is initially slightly enhanced but subsequently significantly inhibited. At the same ion concentration, higher ion valence promotes adsorption more effectively than lower ion valence. Comparative analysis demonstrates that ion concentration exerts a stronger influence on adsorption or desorption behavior than ion valence. The two primary mechanisms driving these phenomena are the impact of ions on the electrostatic potential charge distribution across the graphene surface and their competitive occupation of adsorption sites on graphene. These findings suggest that the amount of aromatic pollutant in wastewater can be precisely controlled by modulating the ionic environment. This study underscores graphene’s potential as a highly recyclable adsorbent material with significant promise for practical applications.

  PublisherDOI

• Strengthening Mechanism of High-Temperature Compression Properties of High Nb–TiAl Alloy by Laser-Directed Energy Deposition

  Coatings · 2025-04-21

  articleOpen access

  High Nb-TiAl alloy components fabricated by laser-directed energy deposition (LDED) exhibit promising applications in aerospace and other high-temperature (HT) fields. It is essential to elucidate the microstructure evolution under HT and high-pressure conditions. In this study, we systematically investigated the room temperature (RT) and HT compression properties of the alloy under various processing parameters, revealing the microstructure evolution during compression. A reduction in laser power (P) decreases the proportion of columnar dendrites while increasing the proportion of epitaxial dendrites, thereby facilitating the transformation of columnar dendrites into equiaxed dendrites. Additionally, lowering the P reduces the size of the α2 + γ lamellar colony (LC) and refines the microstructure of the alloy. The ultimate compressive strength (UCS) of the alloy at RT increased from 1065.5 ± 255.5 MPa at 750 W to 1240.1 ± 104.7 MPa at 450 W. The RT compression fracture is primarily characterized by cleavage surfaces and cleavage steps. The strain rate exhibits a negative correlation with the HT UCS of the alloy. Under conditions of 40% engineering strain, the UCS of the alloy at 900 °C rises from 890.7 ± 98.1 MPa at a strain rate of 0.5 mm/min to 1260.8 ± 91.0 MPa at 5 mm/min. Dislocation and stacking faults can easily occur during the compression process at RT, while dislocations and dynamic recrystallization are more prevalent during compression at 900 °C. Samples subjected to higher strain rates exhibit a lower number of dynamically recrystallized grains, resulting in a higher UCS.

  PublisherOA PDFDOI

• Equiaxed dendrites formation and anisotropy control of high Nb-TiAl alloy by laser additive manufacturing with water-bathed environment

  Intermetallics · 2025-11-05 · 1 citations

  article
  PublisherDOI

• Clinical Observation on the Effectiveness of Combined Anterior and Posterior Cervical Surgery for Cervical Spinal Stenosis with Cervical Injury

  Bone and Arthrosurgery Science · 2025-02-28

  articleOpen access

  Objective: To explore and analyze the clinical effectiveness of combined anterior and posterior cervical surgery for the treatment of cervical spinal stenosis with cervical injury. Methods: From March 2023 to June 2024, 40 patients who received treatment for cervical spinal stenosis with cervical injury in our hospital were selected as the study subjects. They were randomly divided into the experimental group and the control group, with 20 patients in each group. The experimental group underwent combined anterior and posterior cervical surgery, while the control group underwent simple anterior cervical decompression surgery. The changes in clinical indicators and improvement in cervical function before and after surgery were compared and analyzed between the two groups. Results: Following surgical treatment, the clinical indicators in the experimental group improved more significantly than those in the control group. Additionally, the postoperative cervical function improvement in the experimental group was superior to that in the control group. The differences between the two groups were statistically significant (P < 0.05). Conclusion: For patients with cervical spinal stenosis and cervical injury, the combined anterior and posterior cervical surgery approach can effectively improve cervical function, demonstrating significant therapeutic effects. This surgical method is worthy of clinical promotion.

  PublisherOA PDFDOI

• The columnar dendrite and equiaxed dendrite transformation of high Nb-TiAl alloy by laser-directed energy deposition

  Journal of Alloys and Compounds · 2024-01-05 · 14 citations

  article
  PublisherDOI

• Comprehensive Evaluation of the Flexibility of Hydro-Wind-Photovoltaic Power Generation System Based on Hierarchical-Entropy Method

  2024-12-27

  article

  To accurately, comprehensively, and objectively assess the contribution of hydropower to the flexibility of the hydro-wind-photovoltaic power generation system, this study establishes a model of the system and introduces a range of flexibility evaluation indicators, considering both subjective and objective aspects. Subsequently, a sophisticated evaluation method is developed for assessing the flexibility of hydro-windphotovoltaic power generation systems, utilizing the hierarchicalentropy method. The research outcomes underscore the influence of the wind/solar capacity ratio on the flexibility of the hydro-wind-photovoltaic power generation system. Nevertheless, an optimal ratio exists, enabling the system to achieve optimum flexibility. The highest comprehensive evaluation value of system flexibility is achieved when the ratio wind/solar capacity ratio is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1: 2$</tex>, with a score of 84.31. In consonance with this ratio, hydropower emerges as the most adaptable and reliable option, adept at meeting both load demand and the fluctuating requirements of new energy sources to the fullest extent. This study serves as a reference for improving the operational flexibility of the hydro-wind-photovoltaic power generation system and the planning of renewable energy systems.

  PublisherDOI

• New physical insights into the supporting subspace factorization of XMS-CASPT2 and generalization to multiple spin states via spin-free formulation

  The Journal of Chemical Physics · 2024-03-25 · 3 citations

  articleOpen access1st authorCorresponding

  This paper introduces a spin-free formulation of the supporting subspace factorization [C. Song and T. J. Martínez, J. Chem. Phys. 149, 044108 (2018)], enabling a reduction in the computational scaling of the extended multi-state complete active space second-order perturbation (XMS-CASPT2) method for arbitrary spins. Compared to the original formulation that is defined in the spin orbitals and is limited to singlet states, the spin-free formulation in this work treats different spin states equivalently, thus naturally generalizing the idea beyond singlet states. In addition, we will present a new way of deriving the supporting subspace factorization with the purpose of understanding its physical interpretation. In this new derivation, we separate the sources that make CASPT2 difficult into the "same-site interactions" and "inter-site interactions." We will first show how the Kronecker sum can be used to remove the same-site interactions in the absence of inter-site interactions, leading to MP2 energy in dressed orbitals. We will then show how the inter-site interactions can be exactly recovered using Löwdin partition, where the supporting subspace concept will naturally arise. The new spin-free formulation maintains the main advantage of the supporting subspace factorization, i.e., allowing XMS-CASPT2 energies to be computed using highly optimized MP2 energy codes and Fock build codes, thus reducing the scaling of XMS-CASPT2 to the same scaling as MP2. We will present and discuss results that benchmark the accuracy and performance of the new method. To demonstrate how the new method can be useful in studying real photochemical systems, the supporting subspace XMS-CASPT2 is applied to a photoreaction sensitive to magnetic field effects. The new spin-free formulation makes it possible to calculate the doublet and quartet states required in this particular photoreaction mechanism.

  PublisherOA PDFDOI

• Interface Formation Mechanism and Mechanical Properties Analysis of W/Ti6al4v Composites Prepared by Direct Laser Deposition

  SSRN Electronic Journal · 2024-01-01 · 3 citations

  preprintOpen access
  PublisherDOI

Frequent coauthors

• Todd J. Martı́nez

  Stanford University

  91 shared

• Jeffrey B. Neaton

  University of California, Berkeley

  58 shared

• Lee‐Ping Wang

  University of California, Davis

  25 shared

• Edward G. Hohenstein

  Science Wares (United States)

  18 shared

• Christoph Bannwarth

  14 shared

• B. Scott Fales

  Pulse Biosciences (United States)

  14 shared

• Stefan Seritan

  14 shared

• Dongjiang Wu

  Dalian University of Technology

  13 shared

Education

• Ph.D. in Chemistry, Chemistry

  Stanford University

  2018

• B.S. in Chemistry, Chemistry

  Tsinghua University

  2012

Awards & honors

• Francesca Miller Undergraduate Research Award
• R.B. Miller Research, Service, and Mentorship Award
• R. Bryan Miller Summer Graduate Fellowship