A new method for refining the vibrational frequencies and modes on calculation of the vibrational spectra of polymers

1987 ◽  
Vol 46 (5) ◽  
pp. 472-476
Author(s):  
L. A. Gribov ◽  
L. I. Reitblat
Keyword(s):  
Vibrational Spectra ◽  
Vibrational Frequencies ◽  
New Method

Schwingungsspektren von Tetraphosphordekasulfid P4S10/ Vibrational Spectra of Tetraphosphorus decasulfide P4S10

1983 ◽  
Vol 38 (2) ◽  
pp. 163-166 ◽  
Author(s):  
M. Somer ◽  
W. Bues ◽  
W. Brückner
Keyword(s):  
Solid State ◽  
Raman Spectra ◽  
Vibrational Spectra ◽  
Preparation Method ◽  
Vibrational Frequencies ◽  
Molten State ◽  
Polarization Data ◽  
Decomposition Reactions ◽  
Cage Compound ◽  
Tetraphosphorus Decasulfide

Abstract The solid state i.r. and the solid an molten state Raman spectra of the cage compound P4S10 have been recorded. An assignment of the vibrational frequencies, mainly based on polarization data, is proposed. For P4S10 an improved preparation method is reported. During melting the P4S10 units remain unchanged but partly lose terminal sulfur. Thermic decomposition reactions are given. They are reversible.

More accurate determination of vibrational frequencies in calculation of vibrational spectra of polymers

1984 ◽  
Vol 40 (3) ◽  
pp. 290-294
Author(s):  
A. N. Kalirtnikov ◽  
L. A. Gribov ◽  
V. A. Dement'ev
Keyword(s):  
Vibrational Spectra ◽  
Accurate Determination ◽  
Vibrational Frequencies ◽  
Calculation Of Vibrational Spectra

The vibrational spectra of Methane Sulphonyl Chloride and Methane Sulphonyl Fluoride

1953 ◽  
Vol 6 (1) ◽  
pp. 33 ◽  
Author(s):  
NS Ham ◽  
AN Hambly
Keyword(s):  
Vibrational Spectra ◽  
Vibrational Frequencies ◽  
Improved Method ◽  
Infra Red ◽  
Sulphonyl Fluoride

The Raman and infra-red spectra of methane sulphonyl chloride and methane sulphonyl fluoride have been measured. Assignments of the vibrational frequencies of the two molecules have been made ; the frequency 377 cm.-1 is characteristic of the S-Cl linkage and 1210 cm.-1 of the S-F linkage in these compounds. An improved method for the preparation of methane sulphonyl fluoride is described.

Assignment of N=N Vibrational Frequencies and Tautomeric Effects in the Vibrational Spectra of 1-Aryl-3-alkyl-3-hydroxy-triazenes and Their Platinum Complexes

1995 ◽  
Vol 49 (12) ◽  
pp. 1834-1840 ◽  
Author(s):  
A. Scholz ◽  
A. Wokaun
Keyword(s):  
Vibrational Spectra ◽  
Phenyl Ring ◽  
Vibrational Frequency ◽  
Nmr Spectra ◽  
Platinum Complexes ◽  
Vibrational Frequencies ◽  
Ft Raman Spectroscopy ◽  
Ft Ir ◽  
Related Compounds ◽  
Ft Raman

The vibrational frequencies of the N=N stretching mode of 1-aryl-3-alkyl-3-hydroxy-triazenes and their platinum complexes (PtL4; L = triazene) were investigated by FT-IR and FT-Raman spectroscopy. The influence of electron-donating or -withdrawing substituents on the phenyl ring and of different alkyl substituents at the N3 atom on these frequencies was considered. The N=N vibrational frequency is significantly lowered (as a result of the delocalization of the N=N bond over three nitrogen atoms) compared to related compounds. The Pt complexes show a reduced intensity and an increased linewidth in the vibrational spectra. Additionally, the NMR spectra of the 1-aryl-3-alkyl-3-hydroxy-triazenes were recorded in order to show the tautomeric structure of these substances. The hydroxy triazenes preferentially exist in the N1H form. As a consequence, the N=N stretching frequencies of the hydroxy triazenes appear to be influenced by the superposition of two counteracting effects, the delocalization of the N=N bond and tautomerism.

Synthesis and vibrational spectra of some lead(II) halide adducts with O-, S-, and N-donor atom ligands

1976 ◽  
Vol 54 (21) ◽  
pp. 3430-3438 ◽  
Author(s):  
Ivor Wharf ◽  
Thor Gramstad ◽  
Ramesh Makhija ◽  
Mario Onyszchuk
Keyword(s):  
Raman Spectra ◽  
Vibrational Spectra ◽  
Vibrational Frequencies ◽  
Infrared And Raman Spectra ◽  
Donor Atom ◽  
Bidentate Ligands ◽  
Experimental Conditions ◽  
Monodentate Ligands

Lead(II) halides (PbX2 where X = Cl, Br, and I) formed five types of adducts with monodentate (L) and bidentate (LL) ligands: PbX2•L, PbX2•2L, 2PbX2•L, PbX2•LL, and PbX2•2LL, but not all halides and ligands produced each type. Monodentate ligands were dimethylsulphoxide, N,N-dimethylacetamide, N,N-dimethylthioacetamide, thioacetamide, 2,6-dimethyl-γ-pyrone, N-methyl-2-pyridone, N-methyl-2-pyrollidinone, thiourea, pyridine, piperidine, and aniline, while bidentate ligands were ethylenediamine, tetramethylethylenediamine, 1,10-phenanthroline, and 2,2′-bipyridine. Infrared and Raman spectra are reported together with ligand vibrational frequencies shifted by coordination. Under similar experimental conditions qualitative trends in acceptor and donor abilities appeared to be PbI2 > PbBr2 > PbCl2 and S-donors > O-donors, respectively.

EDF2: A Density Functional for Predicting Molecular Vibrational Frequencies

2004 ◽  
Vol 57 (4) ◽  
pp. 365 ◽  
Author(s):  
Ching Yeh Lin ◽  
Michael W. George ◽  
Peter M. W. Gill
Keyword(s):  
Vibrational Spectra ◽  
Density Functional ◽  
Functional Model ◽  
Harmonic Approximation ◽  
Vibrational Frequencies ◽  
Computational Approach ◽  
Numerical Results ◽  
Harmonic Frequencies ◽  
Anharmonic Frequencies ◽  
Computationally Expensive

The majority of calculations of molecular vibrational spectra are based on the harmonic approximation but are compared (usually after empirical scaling) with experimental anharmonic frequencies. Any agreement that is observed in such cases must be attributable to fortuitous cancellation of errors and it would certainly be preferable to develop a more rigorous computational approach. In this paper, we introduce a new density functional model (EDF2) that is explicitly designed to yield accurate harmonic frequencies, and we present numerical results for a wide variety of molecules whose experimental harmonic frequencies are known. The EDF2 model is found to be significantly more accurate than other DFT models and competitive with the computationally expensive CCSD(T) method.

A Robust Non-Self-Consistent Tight-Binding Quantum Chemistry Method for large Molecules

2019 ◽  
Author(s):  
Philipp Pracht ◽  
Eike Caldeweyher ◽  
Sebastian Ehlert ◽  
Stefan Grimme
Keyword(s):  
Density Functional ◽  
Tight Binding ◽  
Computational Cost ◽  
Vibrational Frequencies ◽  
Molecular Structures ◽  
New Method ◽  
Basis Set ◽  
Semiempirical Methods ◽  
Electronic Interaction ◽  
Self Consistent

We propose a semiempirical quantum chemical method, designed for the fast calculation of molecular Geometries, vibrational Frequencies and Non-covalent interaction energies (GFN) of systems with up to a few thousand atoms. Like its predecessors GFN-xTB and GFN2-xTB, the new method termed GFN0-xTB is parameterized for all elements up to radon (Z = 86) and mostly shares well-known density functional tight-binding approximations as well as basis set and integral approximations. The main new feature is the avoidance of the self-consistent charge iterations leading to speed-ups of a factor of 2-20 depending on the size and electronic complexity of the system. This is achieved by including only quantum mechanical contributions up to first-order which are incorporated similar to the previous versions without any pair-specific parameterization. The essential electrostatic electronic interaction is treated by a classical electronegativity equilibration charge model yielding atomic partial charges that enter the electronic Hamiltonian indirectly. Furthermore, the atomic charge-dependent D4 dispersion correction is included to account for long range London correlation effects. Formulas for analytical total energy gradients with respect to nuclear displacements are derived and implemented in the <i>xtb </i>code allowing numerically very precise structure optimizations. The neglect of self-consistent energy terms not only leads to a large gain in computational speed but also can increase robustness in electronically difficult situations because ill-convergence or artificial charge-transfer (CT) is avoided. The comparison of GFN0-xTB and GFN/GFN2-xTB allows dissection of quantum electronic polarization and CT effects thereby improving our understanding of chemical bonding. Compared to the most sophisticated multipole-based GFN2-xTB model (which approaches DFT accuracy for the target properties closely), GFN0-xTB performs slightly worse for non-covalent interactions and molecular structures, while very good results are observed for conformational energies. Vibrational frequencies are obtained less accurately than with GFN/GFN2-xTB but they may still be useful for various purposes like estimating relative thermostatistical reaction energies. Most exceptional is the fact that even relatively complicated transition metal complex structures can be accurately optimized with a non-self-consistent quantum approach. The new method bridges the gap between force-fields and traditional semiempirical methods with its excellent computational cost to accuracy ratio and is intended to explore the chemical space of large molecular systems and solids.<br>

A Robust Non-Self-Consistent Tight-Binding Quantum Chemistry Method for large Molecules

2019 ◽  
Author(s):  
Philipp Pracht ◽  
Eike Caldeweyher ◽  
Sebastian Ehlert ◽  
Stefan Grimme
Keyword(s):  
Density Functional ◽  
Tight Binding ◽  
Computational Cost ◽  
Vibrational Frequencies ◽  
Molecular Structures ◽  
New Method ◽  
Basis Set ◽  
Semiempirical Methods ◽  
Electronic Interaction ◽  
Self Consistent

We propose a semiempirical quantum chemical method, designed for the fast calculation of molecular Geometries, vibrational Frequencies and Non-covalent interaction energies (GFN) of systems with up to a few thousand atoms. Like its predecessors GFN-xTB and GFN2-xTB, the new method termed GFN0-xTB is parameterized for all elements up to radon (Z = 86) and mostly shares well-known density functional tight-binding approximations as well as basis set and integral approximations. The main new feature is the avoidance of the self-consistent charge iterations leading to speed-ups of a factor of 2-20 depending on the size and electronic complexity of the system. This is achieved by including only quantum mechanical contributions up to first-order which are incorporated similar to the previous versions without any pair-specific parameterization. The essential electrostatic electronic interaction is treated by a classical electronegativity equilibration charge model yielding atomic partial charges that enter the electronic Hamiltonian indirectly. Furthermore, the atomic charge-dependent D4 dispersion correction is included to account for long range London correlation effects. Formulas for analytical total energy gradients with respect to nuclear displacements are derived and implemented in the <i>xtb </i>code allowing numerically very precise structure optimizations. The neglect of self-consistent energy terms not only leads to a large gain in computational speed but also can increase robustness in electronically difficult situations because ill-convergence or artificial charge-transfer (CT) is avoided. The comparison of GFN0-xTB and GFN/GFN2-xTB allows dissection of quantum electronic polarization and CT effects thereby improving our understanding of chemical bonding. Compared to the most sophisticated multipole-based GFN2-xTB model (which approaches DFT accuracy for the target properties closely), GFN0-xTB performs slightly worse for non-covalent interactions and molecular structures, while very good results are observed for conformational energies. Vibrational frequencies are obtained less accurately than with GFN/GFN2-xTB but they may still be useful for various purposes like estimating relative thermostatistical reaction energies. Most exceptional is the fact that even relatively complicated transition metal complex structures can be accurately optimized with a non-self-consistent quantum approach. The new method bridges the gap between force-fields and traditional semiempirical methods with its excellent computational cost to accuracy ratio and is intended to explore the chemical space of large molecular systems and solids.<br>

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