A Molecular Orbital Model of Gel-Silica Ir Spectra

1994 ◽  
Vol 346 ◽  
Author(s):  
Taipau Chia ◽  
Jon K. West ◽  
Larry L. Hench
Keyword(s):  
Structural Changes ◽  
Sol Gel ◽  
Peak Position ◽  
Quantum Mechanical ◽  
Thermal Treatments ◽  
Vibrational Modes ◽  
Silica Monoliths ◽  
Spectral Shifts ◽  
Quantum Mechanical Theory ◽  
Semi Empirical

ABSTRACTThe infrared vibrational modes of sol-gel derived optical silica monoliths depend upon thermal treatments and chemical environments, as shown by Fourier transform infrared spectroscopy (FTIR). A semi-empirical quantum mechanical theory (PM-3 in MOPAC 6.1) is used to analyze the structural changes responsible for the spectral shifts. Optimized structures of 2-member, 3-, 4-, 5- and 6-member rings of SiO2 are calculated. The force constants for the molecular bonds in the rings are obtained and converted to the associated vibrational spectra for the rings. The peak position of the asymmetric transverse optical (AS1TO) mode of the rings shifts from 1070 cm−1 for 2-member rings to 1100 cm−1 for 3-member rings, 1150 cnr1 for 4-member rings, 1140 cm−1 for 5-member and 1120 cm−1 for 6-member rings. The IR data show a 38 cm”1 shift of the AS1TO mode as the gel-silica density changes from 1.1 g/cc to 2.2 g/cc. Thus, the intensification and shift of the AS1TO mode in the gel-silica to higher wave-numbers corresponds to a change in the distribution to larger silicate size rings.

scholarly journals Interactions between large molecules pose a puzzle for reference quantum mechanical methods

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yasmine S. Al-Hamdani ◽  
Péter R. Nagy ◽  
Andrea Zen ◽  
Dennis Barton ◽  
Mihály Kállay ◽  
...  
Keyword(s):  
Experimental Information ◽  
Quantum Mechanical ◽  
Interaction Energies ◽  
Small Organic Molecules ◽  
Large Molecules ◽  
Reference Information ◽  
Mechanical Methods ◽  
Non Covalent Interactions ◽  
Semi Empirical ◽  
Covalent Interactions

AbstractQuantum-mechanical methods are used for understanding molecular interactions throughout the natural sciences. Quantum diffusion Monte Carlo (DMC) and coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] are state-of-the-art trusted wavefunction methods that have been shown to yield accurate interaction energies for small organic molecules. These methods provide valuable reference information for widely-used semi-empirical and machine learning potentials, especially where experimental information is scarce. However, agreement for systems beyond small molecules is a crucial remaining milestone for cementing the benchmark accuracy of these methods. We show that CCSD(T) and DMC interaction energies are not consistent for a set of polarizable supramolecules. Whilst there is agreement for some of the complexes, in a few key systems disagreements of up to 8 kcal mol−1 remain. These findings thus indicate that more caution is required when aiming at reproducible non-covalent interactions between extended molecules.

STRUCTURAL, ELECTRONIC AND QSAR PROPERTIES OF THE CYFLUTHRIN MOLECULE: A THEORETICAL AM1 AND PM3 TREATMENT

2006 ◽  
Vol 17 (10) ◽  
pp. 1391-1402 ◽  
Author(s):  
EMİNE DENİZ ÇALIŞIR ◽  
ŞAKİR ERKOÇ
Keyword(s):  
Energy Level ◽  
Gas Phase ◽  
Ground State ◽  
Heat Of Formation ◽  
Tobacco Budworm ◽  
Vibrational Modes ◽  
Lumo Energy ◽  
Deciduous Fruit ◽  
Semi Empirical ◽  
Homo Energy Level

Cyfluthrin is a synthetic cyano-containing pyrethroid insecticide that has both contact and stomach poison action. It is a nonsystemic chemical used to control cutworms, ants, silverfish, cockroaches, mosquitoes, tobacco budworm and many others. Its primary agricultural uses have been for control of chewing and sucking insects on crops such as cotton, turf, ornamentals, hops, cereal, corn, deciduous fruit, peanuts, potatoes, and other vegetables. Cyfluthrin is also used in public health situations and for structural pest control. The structural, vibrational, electronic and QSAR properties of the cyfluthrin molecule in gas phase have been investigated theoretically by performing molecular mechanics method by using MM+ force field, and semi-empirical molecular orbital AM1 and PM3 calculations. The geometry of the molecule has been optimized, infrared spectrum (vibrational modes and intensities) and the electronic properties of the molecule have been calculated in its ground state. According to PM3 calculation, heat of formation of cyfluthrin molecule is about -48.58 kcal/mol (exothermic), which shows that this molecule thermodynamically be stable. The HOMO energy level for this molecule is found to be -9.701 eV and the LUMO energy level is -0.660 eV giving rise to a gap of 9.041 eV, which also indicates that cyfluthrin is thermodynamically stable.

scholarly journals Synthesis and Optical Manifestation of NiO-Silica Nanocomposite

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
S. Chakrabarty ◽  
K. Chatterjee
Keyword(s):  
Sol Gel ◽  
Size Variation ◽  
Average Diameter ◽  
Xrd Analysis ◽  
Peak Position ◽  
Band Gap Energy ◽  
Strong Emission ◽  
Silica Nanocomposites ◽  
Composite Formation ◽  
Silica Nanocomposite

NiO-silica nanocomposites with average diameter ranging from 2–40 nm were prepared by sol-gel method followed by the heat treatment varying from 400°C to 1000°C. The details of morphology and crystalline nature of all the as prepared samples were characterized by TEM, HRTEM, and XRD analysis. The planes obtained from SAED pattern supports the planes originated from XRD study. From the optical absorption study, it is revealed that the band gap energy of NiO can extensively be manipulated by composite formation with silica and the size variation of that nanocomposite. Absorption peak position varies almost linearly with the oxidation temperature of the samples. Photoluminescence spectroscopy reveals that NiO-silica nanocomposite, prepared at 600°C and below, shows strong emission at 3.62 eV, but the nanocomposites with bigger size greatly hinder the effect of selective emissivity.

scholarly journals Study of Spectral and thermal properties of Selenium Diatomic Halides by Semi-empirical Treatment

2008 ◽  
Vol 5 (2) ◽  
pp. 273-277
Author(s):  
Baghdad Science Journal
Keyword(s):  
Potential Energy Curve ◽  
Bond Angle ◽  
Dipole Moments ◽  
Spectroscopic Properties ◽  
Quantum Mechanical ◽  
Energy Curve ◽  
Total Charge ◽  
Net Charge ◽  
Total Charge Density ◽  
Semi Empirical

The spectroscopic properties, potential energy curve, dipole moments, total charge density, Electrostatic potential as well as the thermodynamic properties of selenium diatomic halides have been studied using code Mopac.7.21 and hyperchem, semi-empirical molecular orbital of MNDO-method (modified neglected of differential overlap) of parameterization PM3 involving quantum mechanical semi-empirical Hamiltonian. The relevant molecular parameters like interatomic distance, bond angle, dihedral angle and net charge were also calculated.

The role of the basis set and the level of quantum mechanical theory in the prediction of the structure and reactivity of cisplatin

2012 ◽  
Vol 33 (29) ◽  
pp. 2292-2302 ◽  
Author(s):  
Diego Paschoal ◽  
Bruna L. Marcial ◽  
Juliana Fedoce Lopes ◽  
Wagner B. De Almeida ◽  
Hélio F. Dos Santos
Keyword(s):  
Basis Set ◽  
Quantum Mechanical ◽  
Mechanical Theory ◽  
Quantum Mechanical Theory

scholarly journals [MG49-LiClO4]:[TiO2-SiO2] Polymer Electrolytes: In Situ Preparation and Characterization

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Oon Lee Kang ◽  
Azizan Ahmad ◽  
Nur Hasyareeda Hassan ◽  
Usman Ali Rana
Keyword(s):  
Polymer Electrolytes ◽  
Structural Changes ◽  
Sol Gel ◽  
Ionic Conductivities ◽  
In Situ Techniques ◽  
In Situ Preparation ◽  
Solution Cast ◽  
Gel Technique ◽  
Cast Technique

In the present research, [MG49-LiClO4]:[HNO3-THF/TiO2-SiO2] and [MG49-LiClO4]:[ClHNO2-THF/TiO2-SiO2] polymer electrolytes were first prepared through simple stepwise in situ techniques: sol-gel technique and solution-cast technique. [MG49-LiClO4]:[HNO3-THF/TiO2-SiO2] and [MG49-LiClO4]:[ClHNO2-THF/TiO2-SiO2] polymer electrolytes were then characterized through different experimental techniques. [MG49-LiClO4]:[HNO3-THF/TiO2-SiO2] and [MG49-LiClO4]:[ClHNO2-THF/TiO2-SiO2] polymer electrolytes had exhibited significant structural changes upon different salt concentrations. In the present investigation, [MG49-LiClO4]:[HNO3-THF/TiO2-SiO2] and [MG49-LiClO4]:[ClHNO2-THF/TiO2-SiO2] polymer electrolytes had attained maximum ionic conductivities (σ~10-7 S/cm at ambient temperature; 10−4 S/cm at 100°C) upon 25 wt.% salt insertion. [MG49-LiClO4]:[HNO3-THF/TiO2-SiO2] and [MG49-LiClO4]:[ClHNO2-THF/TiO2-SiO2] polymer electrolytes had exhibited distinct conduction mechanisms in similar experimental configuration. [MG49-LiClO4]:[HNO3-THF/TiO2-SiO2] and [MG49-LiClO4]:[ClHNO2-THF/TiO2-SiO2] polymer electrolytes had exhibited different stability characteristics over certain operational condition.

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