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Showing 1 to 20 of 22 for “"Force constants"”.
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Applications of lattice dynamics theory : calculating vibrational entropy in alloys and dielectric losses in ceramics
… -0.05 - 0.07 kB. Length-dependent transferable force constants are used to predict vibrational entropies in the Au-Cu, Au-Pd, and Cu-Pd systems. The stiffness of these force constants is obtained from a function that depends on bond length; this function is determined by fitting polynomials to a …
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Bonding properties of coordinated polyhedra in molecules and crystals
Force constants and electron density distributions in coordination polyhedra in molecules and crystals are modeled using Hartree-Fock molecular orbital methods. Model bond-stretching force constants calculated for coordination polyhedra in a series of nitride, oxide and sulfide molecules are ~ …
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Spectroscopic and theoretical studies of small molecules.
… precise 13C frequency shifts for use in force field calculations. Subsequent empirical harmonic force field studies for ketene were carried out and 16 out of 19 force constants were determined. Owing to inaccuracies in a large number of the A1 vibrational frequencies and shifts arising …
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Thermal conductivity from first-principles in bulk, disordered, and nanostructured materials
… scattering rate of these processes based on the force constants derived from DFPT, excellent agreement is obtained between computed and measured values of thermal conductivity. The approach predicts that in isotopically pure silicon, more than 90% of the heat is conducted by phonons of mean free …
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Vibrational many-body methods for molecules and extended systems
… existing representations, which are a quartic force field (QFF) and numerical values on a rectilinear grid. We employed a combination of coupled-cluster singles and doubles (CCSD), CCSD with a second-order perturbation correction in the space of triples [CCSD(2)$_\textit{T}$] and in the space …
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Stability of Topological States and Crystalline Solids
… Monte Carlo. By incorporating the matrix of force constants directly into the algorithms, we find that we are able to improve the efficiency and accuracy of atomic relaxation and eigenfrequency calculation. We test the performance on a diverse selection of case studies, with varying …
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Infrared investigation of some octahedral organometalic [sic] carbonyls
… after electrochemical reduction are presented. Force constants are calculated using the Cotton-Kraihanzel force field and the results discussed in terms of sigma and pi-bonding. Infrared spectral data before and after electroche~ical reduction are also reported for a number of iron-olefin …
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Pulsed molecular beam cavity microwave Fourier transform spectroscopy of some fundamental van der Waals dimers and trimers
… T-shaped geometry dominated by pairwise additive forces, in contrast to the previously studied linear complex Ar-ClF. An effective van der Waals bond distance has been obtained, as well as an average vibrational angle for Cl₂. This study has not only confirmed the structure obtained from …
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Investigation of the mechanical properties and phase stability of Ti-transition metal alloys using first-principle calculations
… on the plastic deformation. We calculate elastic constants, stacking fault energies and dislocation core geometries of non-dilute BCC Ti-Mo random alloys. Studies of dislocation core structures have relied on a variety of coupling techniques to manage the far-field strain fields; one very …
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Vibrational studies of tetrahalogenocuprates (II)
… spectrum; and (B) to develop a competent model force field for such study. The analysis produces a physically sensible set of force constants which supports one particular set of assignments. The potential force field developed in the unit cell analysis of Cs₂CuCℓ₄ was extended to the study of …
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Molecular mechanics calculations of tin-bis (triphenylphosphine oxide) complexes
… of adjustments were made to Allinger's M:M2 force·-field ill order to inl.prove its performance in the treatment of these systems. A set of u,nique force constants was introduced for' those terms representing the metal ligand bond lengths, bond angles, and, torsion angles. These were …
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Thermal transport in low dimensional semiconductor nanostructures
… of each nanostructure using DFT, the interatomic force constants and the phonon dispersion relations were calculated using DFPT as implemented in Quantum Espresso. In order to fundamentally understand the effect of atomic arrangements, we calculated the phonon conductance in a ballistic approach …
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Neutron and x-ray scattering studies of layered solids
… ammonia molecules. In addition, the interlayer force constants in this compound are appreciably softer than in its binary counterpart. We then go on to describe quasielastic neutron scattering results for a hydrogenated K-ammonia sample, which show the existence of two separate molecular …
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Lattice Dynamics in Temperature-driven and Photo-induced Phase Transitions
… renormalized second- order and higher-order force-constants. Moreover, pump-probe experiments can now resolved femtosecond atomic dynamics by using an ultrafast laser pulse to excite materials out of equilibrium and then track the Bragg or diffuse intensities with a time-resolved pulse of …
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A theoretical study of metal-organic frameworks
… of the linkers used in MOFs as it controls the force constants around the minima of rotational profiles of isolated MOF linkers. The study also highlighted the importance of the solvent on the relative energies of the linker conformations – this has a potential impact on the synthesis of MOFs. …
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Protein structure prediction and conformational transitions
… constraint weights and TMD with proper force constants successfully simulated the conformational changes of CDK2 phosphorylation, including the formation of the arginine cluster, maintaining the geometrical relationships of the conserved residues, and the characteristic movement of the …
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Diagrammatic many-body methods for anharmonic molecular vibrational properties
… the computation of a large number of anharmonic force constants, and stochastic algorithms which require no stored representation of the PES. This is a significant advance because the computation and storage of the PES is a significant bottleneck in terms of accuracy and computational cost. The …
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First principles and machine learning methods in molecules, fluids, and solids
… used to study molecules where the formalism for force constants matrix is created for the first time using variational and diffusion Monte Carlo, which are the most accurate technique in electronic structure calculation but more resource demanding. We make the atomic relaxation and vibrational …
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Entropy, Energy and Dynamics of Coalescing Spherical and 1D Aerosols
… to remain constant at SPD. The thermodynamic force, represented as *N<sub>∞</sub><sup>5/6</sup>* (where *N<sub>∞</sub>* is the particle number concentration), and the corresponding flux, d*N<sub>∞</sub><sup>−5/6</sup>*/d*t*, are derived from the time evolution of particle concentration at SPD. …
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Luminescence of impurity-activated alkali halides under high pressure
… ratio of the excited and ground electronic state force constants, as a function of pressure for the emission from the high-pressure (sc) phase of KI:Tl-type phosphors. The emission from KI:Tl-type phosphors is known to display a doublet structure, due to both Jahn-Teller interactions and …
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