In the present study, a computational protocol for predicting the Ti-49 NMR chemical shift (δ49Ti) was constructed with our NMR-DKH basis sets for all atoms, including titanium (Ti), which was developed in this work. Thus, computational protocols were proposed considering 55 different DFT functionals using nonrelativistic Hamiltonian. Besides, four-components (4c) calculations employing the relativistic modified Dirac–Kohn–Sham Hamiltonian at GIAO-4c-BLYP/dyall.VDZ level was also considered. In the best protocol, the structures of the 41 Ti(IV) complexes studied, which cover a wide range of δ49Ti ranging from −1389 to +1325 ppm, were optimized at the BLYP/def2-SVP/IEF-PCM (UFF) level and the δ49Ti was calculated at the GIAO-OLYP/NMR-DKH/IEF-PCM (UFF) level, both employing a nonrelativistic Hamiltonian. In this protocol, a mean absolute deviation (MAD) of only 48 ppm and a coefficient of determination (R2) of 0.9888 were found, which represents an excellent agreement, and with lower computational cost, with the MAD of 62 ppm and R2 of 0.9860 obtained with the relativistic full 4c Hamiltonian at GIAO-4c-BLYP/dyall.VDZ, indicating that the proposed protocol with the NMR-DKH basis set is an excellent alternative for the study of Ti-49 NMR. Additionally, a predictive model based on linear regression () was developed, adjusted from 41 complexes and validated in an external set of nine Ti(IV) complexes, presenting a MAD of 48 ppm and confirming the robustness and extrapolation capacity of the proposed protocol.
The rotational dynamics of protonated cyanogen (NCCNH+) is studied for collision with both para (p-) and ortho (o-) hydrogen (H2) in the temperature range K. Such cold collisions with H2 are essential to get state-to-state rate coefficients for rotational transitions of newly detected NCCNH+. First, the ab initio 4D potential energy surface (PES) for NCCNH+-H2 collision is generated at CCSD(T)-F12b level of theory using augmented triple zeta basis, considering rigid rotor approximation. The 4D PES is further fitted into a neural network (NN) model to augment the PES by folds. The PES is then expanded using bispherical harmonics functions to get radial terms, which are expressed as analytic functions. The cross-sections and rate coefficients for NCCNH+ are calculated using the exact close-coupling method for rotational states up to , considering both p- and o-H2 collisions. The rates show similar behavior to the earlier studied NCCN-H2 collision, with the latter having larger rate coefficients.
We have combined the linear-scaling divide-and-conquer (DC) method with the semi-empirical extended tight-binding (xTB) method to develop a general-purpose large-scale quantum molecular dynamics simulation platform called DCxTBMD. Although the DC method is a fragmentation-based acceleration scheme, it is possible to perform highly accurate calculations even when adopting formal grid-based fragmentation, thanks to the mechanism called the buffer region. The program was developed by incorporating xTB Hamiltonian construction modules in the xTB program into the DCDFTBK package, a DC-based density functional tight-binding (DFTB) calculation suite. The accuracy and computational time, including the parallel scalability, of the present method were investigated on the Japanese supercomputer Fugaku, and it was found that the present method is suitable for the efficient calculation of large systems, including multiple heteroelements. We further implemented the energy gradient of the present method to enable the molecular dynamics simulation of such systems.
The solvation free energy is a fundamental property of a solute directly related to solubility, which in turn is critical for processes ranging from pharmaceutical to materials manufacturing. We seek to develop efficient strategies to predict the solvation free energy, knowing only molecular structure, using electronic structure calculations with the uESE continuum solvation model. Benchmarking on the Minnesota Solvation Database, single conformations generated using the molecular mechanics force field MMFF94 yielded predictive accuracy comparable to reference gas-phase optimized geometries obtained with electronic structure calculations. Surprisingly, exploring multiple conformations did not consistently improve predictions, suggesting uESE performs well with a single representative input. Evaluation on the independent dGsolvDB1 dataset demonstrated reasonable predictive ability with single molecular mechanics-generated conformations and some generalizability to novel chemical space. Our findings indicate that combining fast molecular mechanics-based structure generation with uESE offers a promising approach for efficient and reasonably accurate solvation free energy predictions, with accuracy comparable to or exceeding that of far more computationally intensive methods like explicit solvent molecular dynamics, supporting its utility in high-throughput screening and machine learning for solubility prediction.
This review presents a comprehensive overview of global optimization techniques applied to the prediction of chemical structures, including molecular conformations, crystal polymorphs, and reaction pathways. These approaches typically involve a two-step process: a global search to identify candidate structures, followed by local refinement to determine the most stable configurations. Global optimization methods are commonly grouped into two categories, known as stochastic and deterministic methods, based on their exploration strategies and underlying theoretical principles. A historical perspective highlights the progression of these methods, from early foundational algorithms to more advanced and efficient modern techniques. For each category, key algorithmic frameworks are outlined, widely used software tools are discussed, and representative applications are examined, such as conformer sampling, cluster structure prediction, and surface adsorption. The review concludes by considering future directions, including the integration of accurate quantum methods, the development of flexible hybrid algorithms, and the use of quantum computing to address increasingly complex chemical problems.
This review highlights the design and applications of various types of neutral organic superbases, a relatively new and widely adopted class of Brønsted bases. These superbases offer complementary properties to conventional inorganic bases and have found increasing commercial application in modern synthetic methodologies. The recent advances in the computational design, synthesis, and catalytic behavior of organic superbases have been summarized. This article would embolden the development of novel, highly effective, and selective catalysts that enable efficient chemical transformations under metal-free conditions.
Tubular g-C3N4 nanotubes (CNNTs), experimentally realizable counterparts of 2D g-C3N4, present promising opportunities for tuning electronic, optical, and mechanical properties, which remain largely underexplored. In this work, density functional theory calculations are utilized to evaluate the band gaps and elastic moduli of CNNTs with varying diameters and chiralities under applied strain. The results reveal that the Young's moduli of these CNNTs span from 40 to 230 GPa, while the band gaps show an inverse correlation with the aspect ratio. This systematic study advances the fundamental understanding of CNNTs and provides valuable insights for the rational design of nanostructured materials aimed at applications including photocatalysis and electrocatalysis.
The hetero coalescences of the Cu147 and Ag147 clusters at room temperature and 1300 K have been simulated by molecular dynamics approaches within embedded atom method framework, and then the structural transformation of alloying clusters formed after the coalescence is investigated during heating and cooling. The activation energy is used to describe the potential barriers that need to be overcome to carry out the merger, the potential energy characterizes the structural transition the free energy difference reflects the driving force for the coalescence of the clusters. The simulation results show that different contacting modes and different distances between the two clusters at 300 K affect the heterogeneously coalescing processes and the alloying clusters formed, and that the increase in temperature greatly affects the motion of the atoms as well as the atomic packing structures within the alloying clusters. At the beginning of coalescence, the two clusters are in contact with each other, forming a connecting neck, and the Ag atoms diffuse along the surface of the Cu clusters. With the increase of temperature, Ag atoms gradually wrap around the Cu clusters, and the Cu clusters also undergo structural changes at high temperatures, and the Cu-Ag alloy clusters with different initial cohesive distances and cohesive orientations show different packing patterns. For the Cu-Ag clusters obtained via high-temperature coalescence, the cooling stage not only exhibits distinctly different structural transformation processes, but the structural transformation temperatures corresponding to each process also show significant differences.
Core-shell (CS) particle consisting of Pt shell and base metal core is one of promising candidates of excellent electrode catalyst for fuel cell, because it is highly active and highly stable like Pt particle but less expensive than Pt particle. However, its stability has been unclear. Herein, icosahedral M13@Pt42 (M = 3d transition metals, Sc to Cu) CS particles consisting of Pt42 shell and M13 core are systematically investigated using DFT calculations. The CS structures of Co13@Pt42, Ni13@Pt42, and Cu13@Pt42 are calculated to be more stable than their non-core-shell (NCS) structures in which one 3d metal atom of the M13 core is exchanged with one Pt atom of the Pt42 shell. For Sc13Pt42, Ti13Pt42, V13Pt42, Cr13Pt42, Mn13Pt42, and Fe13Pt42, on the other hand, the NCS structure is more stable than the CS one. Small deformation energy of the Pt42 shell compared to that of the Pt41M shell and small stabilization energy by Pt–M exchange between the Pt42 shell and the M13 core are particularly important for stabilizing the CS structure. Late 3d metal elements in the first transition series of the periodic table such as Co, Ni, and Cu are suitable for producing a stable M13@Pt42 CS particle because their electronegativities are larger than those of the early and middle 3d transition metal elements and their atomic sizes are smaller than those of the early 3d metal elements such as Sc and Ti atoms. O2 adsorption to M13@Pt42 (M = Co, Ni, and Cu) CS particle occurs at the edge Pt atom and the vertex Pt atom in a side-on manner. The adsorption energies of O2 molecule to Co13@Pt42, Ni13@Pt42, and Cu13@Pt42 CS particles are smaller than that to Pt55 particle, indicating that the M13 core decreases the reactivity of the Pt42 shell for O2 adsorption.
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