Article
Chemistry, Physical
Yu-Shu Wang, Sabyasachi Kar, Yew Kam Ho
Summary: The dipole transition elements and oscillator strengths for the doubly excited states of the helium atom were investigated using correlated exponential wavefunctions. The results obtained were comparable with available data, and some dipole transitions for S-P and P-D states were reported for the first time. The predictions of this work are of experimental interest.
CHEMICAL PHYSICS LETTERS
(2021)
Article
Chemistry, Physical
Jiachen Li, Zehua Chen, Weitao Yang
Summary: This article introduces a method to calculate accurate energies using renormalized singles (RS) in multireference density functional theory (DFT). The method improves the original approach by using a modified RS Hamiltonian to calculate two-electron addition energies, providing accurate energy calculations for both ground and excited states.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2022)
Article
Chemistry, Physical
Jiaxin Ning, Donald G. Truhlar
Summary: Cerium plays crucial roles in catalysis due to spin-orbit coupling and open-shell effects, making quantum mechanical calculations challenging. Various multiconfigurational and single-configurational methods were used to study the spin states of Ce+ and the bond energy of CeH+. CASPT2 and GAM methods were found to be the most accurate in predicting the excitation energy and bond energy for Ce+ and CeH+, respectively.
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
(2021)
Article
Chemistry, Physical
Nuno M. S. Almeida, Timothe R. L. Melin, Angela K. Wilson
Summary: High level multireference calculations were performed on LuF, including 132 states and discussing dissociation channels and excited states. Various methods were used to calculate dissociation energies at different theory levels, with the best prediction obtained using coupled-cluster methods and including a relativistic treatment of electrons.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Physics, Multidisciplinary
Yuhao Zhu, Rui Jin, Yong Wu, Jianguo Wang
Summary: The scattering matrices of e + N+ in discrete energy regions are calculated using the eigenchannel R-matrix method, and good parameters of multichannel quantum defect theory (MQDT) are obtained from the analytical continuation property. All discrete energy levels for N are accurately calculated using MQDT. The obtained optical oscillator strengths provide rich data for the diagnostic analysis of plasma.
Article
Chemistry, Physical
Pattarapon Moonkaen, Jacob M. Finney, Anne B. McCoy
Summary: The structure and spectra of ethyl cation and its deuterated analogues are studied using diffusion Monte Carlo method. The ground state of H+(C2H4) is found to be localized near the minimum energy configuration where the excess proton is in a bridging configuration. Deuteration affects the vibrational motion of the bridging proton. Excited states and their frequencies are calculated and compared with experiments.
JOURNAL OF PHYSICAL CHEMISTRY A
(2023)
Article
Chemistry, Physical
Pattarapon Moonkaen, Jacob M. Finney, Anne B. McCoy
Summary: The structure and spectra of ethyl cation and its deuterated analogues have been studied using diffusion Monte Carlo (DMC). The ground state wave function of H+(C2H4) is localized near the minimum energy configuration with a large amplitude of vibrational motions. Deuteration of the bridging proton reduces its motion amplitude, while deuteration of ethylenic hydrogen atoms has little effect. Excited states and their frequencies have also been calculated.
JOURNAL OF PHYSICAL CHEMISTRY A
(2023)
Article
Chemistry, Physical
Yann Damour, Pierre-Francois Loos, Rau'l Quintero-Monsebaiz, Michel Caffarel, Denis Jacquemin, Fabris Kossoski, Anthony Scemama
Summary: We computed ground- and excited-state dipole moments and oscillator strengths using the Configuration Interaction using a Perturbative Selection made Iteratively (CIPSI) method, obtaining near-FCI estimates. By calculating 35 ground- and excited-state properties in 11 small molecules, we assessed the accuracy of high-order coupled-cluster (CC) calculations with up to quadruple excitations. Our results show that increasing the excitation degree of the CC expansion reduces the average error with respect to the near-FCI reference values by approximately 1 order of magnitude.
JOURNAL OF CHEMICAL THEORY AND COMPUTATION
(2023)
Article
Engineering, Multidisciplinary
Noriyuki Kushida, Hiroshi Okuda
Summary: The study introduces a new method that updates the matrix using information obtained through Krylov solver computation, combined with L-BFGS Hessian matrix update and ORTHOMIN residual method. Performance tests show significant improvements in convergence rate and computational time compared to AMG.
INTERNATIONAL JOURNAL OF COMPUTATIONAL METHODS
(2021)
Article
Chemistry, Physical
Paulina Maczugowska, Paulina Zawadzka, Krzysztof Halagan, Marcin Pastorczak, Joanna Sadlej, Marcin Kozanecki
Summary: In this study, water clusters formed in organic liquid matrices with different polarities were investigated using infrared absorption spectroscopy, Molecular Dynamics simulations, and Density Functional Theory calculations. The correlation between experiments and computations at a high level of accuracy was presented for the first time. The results revealed that a higher polarity of the organic matrix favored the formation of stable, small, and cyclic water clusters, while water molecules in nonpolar matrices tended to undergo phase separation on a macroscopic scale. The size of the water clusters strongly depended on the water content in the matrix.
JOURNAL OF MOLECULAR LIQUIDS
(2023)
Article
Engineering, Aerospace
Abdelaaziz Bouziane, Mohammed Amin Ferdi, Mourad Djebli
Summary: The study focuses on the vibrational excited levels of nitric oxide during daytime at altitudes between 80 and 200 km. Using a kinetic-fluid model, density profiles of major ions and nitrogen atoms are analyzed, showing that vibrational excitation of nitric oxide is strongly influenced by solar control, reaching peak values near noon. Data from the SABER satellite instrument confirm the numerical results.
ADVANCES IN SPACE RESEARCH
(2022)
Article
Chemistry, Physical
S. Thanos, A. K. Theophilou, P. N. Moustanis
Summary: In this work, the maximum value of a functional is searched for, using a Slater Determinant and the exact Hamiltonian of an atom or molecule. The procedure is repeated in the orthogonal subspace to find lower energy states and higher excited states. The method is applied to determine the energies of various configurations.
Article
Mathematics, Interdisciplinary Applications
Somnath Roy, Anirban Ray, Roy Chowdhury
Summary: This study focuses on a periodically damped van der Pol oscillator, particularly on the formation of sub harmonic resonance and the transition of its motion to the chaotic domain. The slow fast separation technique is used to analytically identify the domain of these resonances by removing secular terms. The same method is used in conjunction with the multiple scale technique to identify the occurrence of Hopf bifurcation and the generation of limit cycle. Additionally, the Hamiltonian nature of the system is utilized to determine the threshold parameter values for the onset of chaos using the Melnikov function. The hysteresis structure change due to the periodic damping is explicitly determined. In the chaotic regime, characterization is done using Lyapunov exponent, Poincare map, and phase space attractor structure.
CHAOS SOLITONS & FRACTALS
(2023)
Article
Chemistry, Organic
Xin Ma, Erlu Feng, Hanning Jiang, Victoria M. Boulos, Jinshan Gao, John J. Nash, Hilkka Kenttamaa
Summary: The gaseous 2,6-didehydropyridinium cation and its derivatives undergo proton transfer reactions from their lowest-energy excited triplet states, potentially due to unfavorable molecular orbital interactions in their singlet ground states. These cations have smaller singlet-triplet splittings compared to other analogues, likely due to reduced orbital overlap caused by the presence of a nitrogen atom. Both singlet and triplet states are believed to be generated upon formation of biradicals, with triplet states leading to faster proton transfer rates unless heavy atoms are present in the biradicals.
JOURNAL OF ORGANIC CHEMISTRY
(2021)
Article
Physics, Multidisciplinary
JianJun Qi, YuYao Bai, QianQian Guo, Yong-Chang Han, Maksim B. Shundalau
Summary: Based on high-level ab initio calculations, accurate potential energy curves and spectroscopic parameters of Li-2 were obtained, with vibrational energy levels calculated for two electronic states. The results are in good agreement with experimental data, providing reliable theoretical references for further studies on the Li-2 dimer.
COMMUNICATIONS IN THEORETICAL PHYSICS
(2021)