journal
https://read.qxmd.com/read/38504619/can-iron-porphyrins-behave-as-single-molecule-magnets
#21
JOURNAL ARTICLE
Aritra Mukhopadhyaya, Md Ehesan Ali
The study of magnetic properties, especially the magnetic anisotropy of iron-porphyrin complexes employing multiconfigurational methods, is quite challenging due to many strongly correlated electrons in nearly degenerate orbitals. However, a prerequisite for observing the magnetic anisotropy and slow magnetization relaxation, the zero-field splitting parameter, D , was experimentally observed decades ago for halide-based axially ligated penta-coordinate Fe(III)-porphyrins. In these complexes, the signs of D were reported mostly as positive; in a few cases, inconclusive signs of the D parameter were also mentioned...
March 20, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38504122/quantum-chemistry-study-of-the-photophysical-properties-of-4-thiouracil-and-comparisons-with-2-thiouracil
#22
JOURNAL ARTICLE
Miriam Navarrete-Miguel, Angelo Giussani, Mercedes Rubio, Martial Boggio-Pasqua, Antonio Carlos Borin, Daniel Roca-Sanjuán
DNA in living beings is constantly damaged by exogenous and endogenous agents. However, in some cases, DNA photodamage can have interesting applications, as it happens in photodynamic therapy. In this work, the current knowledge on the photophysics of 4-thiouracil has been extended by further quantum-chemistry studies to improve the agreement between theory and experiments, to better understand the differences with 2-thiouracil, and, last but not least, to verify its usefulness as a photosensitizer for photodynamic therapy...
March 19, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38502940/adaptive-force-field-parameter-optimization-for-expanding-reaction-simulations-within-wide-ranged-temperature
#23
JOURNAL ARTICLE
Qingfu Huang, Guixiang Li, Junjie Wang, Bo Niu, Fang Fang, Dongliang Quan, Donghui Long, Yayun Zhang
Large-scale and long-term simulation of chemical reactions are key research topics in computational chemistry. However, there are still difficulties in simulating high-temperature reactions, such as polymer thermal decomposition. Herein, we introduce an adaptive potential parameter optimization framework designed to automatically fine-tune parameters, and the application of it to optimize ReaxFF parameters enhances the accuracy of chemical reaction simulations conducted at experimental temperatures. To achieve this, we leverage the power of Random Forests and interpretable machine learning techniques that enable the identification and selection of parameters that exert a substantial influence on the target attribute...
March 19, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38502933/mechanistic-insights-into-the-proton-transfer-and-substitution-dynamics-of-n-atom-center-reactions-a-study-of-ch-3-o-with-nh-2-cl
#24
JOURNAL ARTICLE
Xu Liu, Huining Feng, Rui Li, Qiuju Zhang, Yang Wu, Boxue Pang
Bimolecular substitution reactions involving N as the central atom have continuously improved our understanding of substitution dynamics. This work used chemical dynamics simulations to investigate the dynamics of NH2 Cl with N as the central atom and the multiatomic nucleophile CH3 O- and compared these results with the F- + NH2 Cl reaction. The most noteworthy difference is in the competition between proton transfer (PT) and the SN 2 pathways. Our results demonstrate that, for the CH3 O- + NH2 Cl system, the PT pathway is considerably more favorable than the SN 2 pathway...
March 19, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38501814/zero-field-splitting-tensor-of-the-triplet-excited-states-of-aromatic-molecules-a-valence-full-%C3%AF-complete-active-space-self-consistent-field-study
#25
JOURNAL ARTICLE
Katsuki Miyokawa, Yuki Kurashige
A method to predict the D tensor in the molecular frame with multiconfigurational wave functions in large active space was proposed, and the spin properties of the lowest triplets of aromatic molecules were examined with full-π active space; such calculations were challenging because the size of active space grows exponentially with the number of π electrons. In this method, the exponential growth of complexity is resolved by the density matrix renormalization group (DMRG) algorithm. From the D tensor, we can directly determine the direction of the magnetic axes and the ZFS parameters, D - and E -values, of the phenomenological spin Hamiltonian with their signs, which are not usually obtained in ESR experiments...
March 19, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38500343/non-irc-mechanism-of-bimolecular-reactions-with-submerged-barriers-a-case-study-of-si-h-2-o-reaction
#26
JOURNAL ARTICLE
Ruilin Li, Tengyu Gao, Ping Zhang, Anyang Li
Chemical reactions with submerged barriers may feature interesting dynamic behaviors that are distinct from those with substantial barriers or those entirely dominated by capture. The Si+ + H2 O reaction is a prototypical example, involving even two submerged saddle points along the reaction path: one for the direct dissociation of H (H-dissociation SP) and another for H migration from the O-side to the Si-side (H-migration SP). We investigated the intricacies of this process by employing quasi-classical trajectory calculations on an accurate, full-dimensional ab initio potential energy surface...
March 18, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38489755/rovibrational-energies-of-13-c-16-o-2-determined-with-kilohertz-accuracy
#27
JOURNAL ARTICLE
Zi-Tan Zhang, Fang-Hui Cao, Shan Jiang, An-Wen Liu, Yan Tan, Y R Sun, Shui-Ming Hu
Accurate spectroscopic data of carbon dioxide are widely used in many important applications, such as carbon monitoring missions. Here, we present comb-locked cavity ring-down saturation spectroscopy of the second most abundant isotopologue of CO2 , 13 C16 O2 . We determined the positions of 88 lines in three vibrational bands in the 1.6 μm region, 30011e/30012e/30013e-00001e, with an accuracy of a few kHz. Based on the analysis of combination differences, we obtained for the first time the ground-state rotational energies with kHz accuracy...
March 15, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38489510/comparison-of-variational-and-perturbative-spin-orbit-coupling-within-two-component-casscf
#28
JOURNAL ARTICLE
Can Liao, Chad E Hoyer, Rahoul Banerjee Ghosh, Andrew J Jenkins, Stefan Knecht, Michael J Frisch, Xiaosong Li
The modeling of spin-orbit coupling (SOC) remains a challenge in computational chemistry due to the high computational cost. With the rising popularity of spin-driven processes and f-block metals in chemistry and materials science, it is incumbent on the community to develop accurate multiconfigurational SOC methods that scale to large systems and understand the limits of different treatments of SOC. Herein, we introduce an implementation of perturbative SOC in scalar-relativistic two-component CASSCF (srX2C-CASSCF-SO)...
March 15, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38489273/ion-spectroscopy-reveals-structural-difference-for-proteins-microhydrated-by-retention-and-condensation-of-water
#29
JOURNAL ARTICLE
Andrei Zviagin, Oleg V Boyarkin
Protein ubiquitin in its +7 charge state microhydrated by 5 and 10 water molecules has been interrogated in the gas phase by cold ion UV/IR spectroscopy. The complexes were formed either by condensing water onto the unfolded bare proteins in a temperature-controlled ion trap or by incomplete dehydration of the folded proteins. In the case of cryogenic condensation, the UV spectra of the complexes exhibit a resolved vibrational structure, which looks similar to the spectrum of bare unfolded ubiquitin. The spectra become, however, broad-band with no structure when complexes of the same size are produced by incomplete dehydration under soft conditions of electrospray ionization...
March 15, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38485448/ultrafast-computational-screening-of-molecules-with-inverted-singlet-triplet-energy-gaps-using-the-pariser-parr-pople-semiempirical-quantum-chemistry-method
#30
JOURNAL ARTICLE
Kjell Jorner, Robert Pollice, Cyrille Lavigne, Alán Aspuru-Guzik
Molecules with an inverted energy gap between their first singlet and triplet excited states have promising applications in the next generation of organic light-emitting diode (OLED) materials. Unfortunately, such molecules are rare, and only a handful of examples are currently known. High-throughput virtual screening could assist in finding novel classes of these molecules, but current efforts are hampered by the high computational cost of the required quantum chemical methods. We present a method based on the semiempirical Pariser-Parr-Pople theory augmented by perturbation theory and show that it reproduces inverted gaps at a fraction of the cost of currently employed excited-state calculations...
March 14, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38484711/efficient-method-for-numerical-calculations-of-molecular-vibrational-frequencies-by-exploiting-sparseness-of-hessian-matrix
#31
JOURNAL ARTICLE
Xingyu Yang, Haitao Ma, Qing Lu, Wensheng Bian
Molecular vibrational frequency analysis plays an important role in theoretical and computational chemistry. However, in many cases, the analytical frequencies are unavailable, whereas frequency calculations using conventional numerical methods are very expensive. In this work, we propose an efficient method to numerically calculate the frequencies. Our main strategies are to exploit the sparseness of the Hessian matrix and to construct the N -fold two-variable potential energy surfaces to fit the parabola parameters, which are later used for the construction of Hessian matrices...
March 14, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38484115/leveraging-machine-learning-to-predict-the-atmospheric-lifetime-and-the-global-warming-potential-of-sf-6-replacement-gases
#32
JOURNAL ARTICLE
Guobin Zhao, Haewon Kim, Changwon Yang, Yongchul G Chung
The global warming potential (GWP) is a relative measure of the capability of a molecule to trap the Earth's infrared radiation as heat. The measurement or prediction of the GWP of a molecule is based on two factors: the radiative efficiency and atmospheric lifetime of a molecule. While the calculation of the radiative efficiency of a molecule using the computational chemistry approach, such as density functional theory (DFT), is well-established and robust, the development of a computational approach to estimate the atmospheric lifetime remains challenging and limited to date...
March 14, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38484111/many-body-expansion-based-on-variational-quantum-eigensolver-and-deflation-for-dynamical-correlation
#33
JOURNAL ARTICLE
Enhua Xu, Yuma Shimomoto, Seiichiro L Ten-No, Takashi Tsuchimochi
In this work, we utilize the framework of many-body expansion (MBE) to decompose electronic structures into fragments by incrementing virtual orbitals, aiming to accurately solve the ground and excited state energies of each fragment using the variational quantum eigensolver and deflation algorithms. While our approach is primarily based on unitary coupled cluster singles and doubles (UCCSD) and its generalization, we also introduce modifications and approximations to conserve quantum resources in MBE by partially generalizing the UCCSD operator and neglecting the relaxation of the reference states...
March 14, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38483535/strengthening-of-noncovalent-bonds-caused-by-internal-deformations
#34
JOURNAL ARTICLE
Steve Scheiner
It is usually assumed that the maximal noncovalent bond strength is achieved by full geometry optimization of the geometry of the dyad. Density functional theory calculations show this not to be the case. A number of systems are considered that include osme, tetrel, pnictogen, and chalcogen bonds, involving both σ- and π-holes, as well as hypervalency. By suitable adjustment of the bond angles within the Lewis acid, the base can be drawn closer than in the optimized structure, with an accompanying substantial strengthening of the noncovalent bond, by more than 10 kcal/mol in some cases...
March 14, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38483325/consecutive-reduction-of-five-carbon-dioxide-molecules-by-gas-phase-niobium-carbide-cluster-anions-nb-3-c-4-unusual-mechanism-for-enhanced-reactivity-by-the-carbon-ligands
#35
JOURNAL ARTICLE
Yi-Heng Zhang, Jia-Bi Ma
Studying the cleavage of the C═O bond during CO2 activation at room temperature is highly significant for comprehending the CO2 conversion processes. Herein, mass spectrometry experiments and density functional theory calculations indicate that the niobium carbide anions Nb3 C4 - can continuously convert five CO2 molecules to CO under thermal collision conditions, while the other clusters with less carbon ligands Nb3 C1-3 - reduce fewer CO2 molecules. Size-dependent reactivity of Nb3 C1-4 - cluster anions toward CO2 is observed...
March 14, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38483190/a-story-of-three-levels-of-sophistication-in-scf-ks-dft-orbital-optimization-procedures
#36
JOURNAL ARTICLE
Daniel Sethio, Emily Azzopardi, Ignacio Fdez Galván, Roland Lindh
In this work, three versions of self-consistent field/Kohn-Sham density functional theory (SCF/KS-DFT) orbital optimization are described and benchmarked. The methods are a modified version of the geometry version of the direct inversion in the iterative subspace approach (which we call r-GDIIS), the modified restricted step rational function optimization method (RS-RFO), and the novel subspace gradient-enhanced Kriging method combined with restricted variance optimization (S-GEK/RVO). The modifications introduced are aimed at improving the robustness and computational scaling of the procedures...
March 14, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38483142/molecular-geometry-impact-on-deep-learning-predictions-of-inverted-singlet-triplet-gaps
#37
JOURNAL ARTICLE
Leonardo Barneschi, Leonardo Rotondi, Daniele Padula
We present a deep learning model able to predict excited singlet-triplet gaps with a mean absolute error (MAE) of ≈20 meV to obtain potential inverted singlet-triplet (IST) candidates. We exploit cutting-edge spherical message passing graph neural networks designed specifically for generating 3D graph representations in molecular learning. In a nutshell, the model takes as input a list of unsaturated heavy atom Cartesian coordinates and atomic numbers, producing singlet-triplet gaps as output. We exploited available large data collections to train the model on ≈40,000 heterogeneous density functional theory (DFT) geometries with available ADC(2)/cc-pVDZ singlet-triplet gaps...
March 14, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38482814/dependence-of-uranium-oxide-polymorphism-on-plasma-synthesis-conditions
#38
JOURNAL ARTICLE
Emily N Weerakkody, Batikan Koroglu, Zurong Dai, Kate E Rodriguez, Enrica Balboni
We synthesized uranium oxide nanoparticles using a plasma flow reactor (PFR) and studied the effects of three different experimental parameters on the resulting morphologies and speciation of the particles: (1) collection duration, (2) collection substrate temperature, and (3) radial collection position due to radial temperature gradients in the PFR. We also induced three distinct temperature histories along the axis of the plasma flow reactor by varying the gas flow rates downstream of the plasma torch. Transmission electron microscopy (TEM) analyses of collected particles showed two phases of uranium oxides (fcc-UO2 and α-UO3 )...
March 14, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38480504/supercollisions-of-nacl-nacl-on-an-accurate-full-dimensional-potential-energy-surface
#39
JOURNAL ARTICLE
Tianze Peng, Yuyao Bai, Jianjun Qi, Yan-Lin Fu, Yong-Chang Han, Bina Fu, Dong H Zhang
An accurate, global, full-dimensional potential energy surface (PES) of NaCl + NaCl has been constructed by the fundamental invariant-neural network (FI-NN) fitting based on roughly 13,000 ab initio energies at the level of CCSD(T)-F12a/aug-cc-pVTZ, with the small fitting error of 0.16 meV. Extensive quasiclassical trajectory (QCT) calculations were performed on this PES to investigate the energy transfer process of the NaCl + NaCl collision at four different collision energies. Various quantities were obtained, including the cross-sections, energy transfer probability, average energy transfer, and collision lifetime...
March 13, 2024: Journal of Physical Chemistry. A
https://read.qxmd.com/read/38479752/predicting-rate-constants-of-alkane-cracking-reactions-using-machine-learning
#40
JOURNAL ARTICLE
Yu Zhang, Min Xia, Hongwei Song, Minghui Yang
Calculating the thermal rate constants of elementary combustion reactions is of great importance in theoretical chemistry. Machine learning has become a powerful, data-driven method for predicting rate constants nowadays. Recently, the molecular similarity combined with the topological indices were proposed to represent the hydrogen abstraction reactions of alkane [ J. Chem. Inf. Model . 2023 , 63 , 5097-5106], which are, however, not applicable to alkane cracking reactions, another important class of combustion reactions, due to the cleavage of the C-C bond...
March 13, 2024: Journal of Physical Chemistry. A
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