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In this paper, we used the 8-band k$\cdot$p model with valence force field considerations to investigate the effect of size and shape on electronic and optical properties of cadmium selenide quantum dots. Major factors related to their properties including band mixing probabilities, spatial charge distributions, transition matrix elements and Fermi factors were studied. Volumetrically larger CdSe dots were found to have smaller band-gaps but higher transition matrix elements and Fermi factors. The maximum optical gain for dots was observed to have an initially positive and then negative correlation with their real-space size as a result of combined effects of various factors. For the shape effects, cubic dots were found to have smaller band-gaps, Fermi factors and transition matrix elements than spherical dots due to higher level of asymmetry and different surface effects. Consequently, cubic dots have lower emission energy, smaller amplification. The occurrence of near E1-H1 transition broadens the gain spectrum of cubic dots. Cubic and spherical dots are both proven to be promising candidates for optical devices under visible range. We have demonstrated that size and shape change could both effectively alter the properties of quantum dots and therefore recommend consideration of both when optimizing the performance for any desired application., Comment: Published in Optik - International Journal for Light and Electron Optics (8 pages, 10 figures), 2017

Molecular dynamics (MD) simulations were carried out to investigate the conformations of fourth generation polyamidoamine (G4 PAMAM) dendrimer-encapsulated Au nanoparticles (AuNPs) of different sizes at different pH conditions. The consistent valence force field (CVFF) was used to model the interaction between the atoms of G4 PAMAM dendrimer and water molecules as well as their interactions with the Au atoms of AuNP. The many-body tight-binding potential was adopted to describe the interaction between Au atoms. The simulation results show a single G4 PAMAM dendrimer can only partially cover the AuNP when its diameter is larger than 2.3 nm. According to the variations of radius of gyration ( R g ) values, the conformations of PAMAM dendrimers become more compact after covering the AuNP at neutral pH. According to the Stokes–Einstein (SE) relation and the diffusion coefficients obtained by the Einstein equation, it was proposed that both the PAMAM dendrimer conformation and the interaction strength between the PAMAM/AuNP and water molecules have significant influences on the diffusion behaviors of PAMAM/AuNP systems.

Spinodal decomposition ranges of wurtzite and zinc blende Zn B VI x O 1− x ( B VI =S, Se, Te) alloys from 0 °C to 1000 °C are represented. The strain energy was estimated in the framework of the valence force field model. All considered alloys have the very extensive decomposition zones in spite of the coherency strain energy. Spinodal decomposition in wurtzite alloys should occur in planes with an orientation that depends on the lattice parameters, stiffness coefficients and composition. Zinc blende alloys posses the larger zones and decomposition should take place only in the {100} oriented planes. Spinodal decomposition ranges are 0.02 x x x x O 1− x , ZnSe x O 1− x and ZnTe x O 1− x , respectively, at RT.

We have studied, by computer simulation, some static and vibrationnal proprieties of SiGe/Si islands. We have used a Valence Force Field combined to Monte Carlo technique to study the growth of Ge and SiGe on (001)Si substrates. We have focalised on the case of large pyramidal islands presenting (113) facets on the free (001)Si surface with various non uniform composition inside the islands. The deformation inside the islands and Raman spectroscopy are discussed.

We discuss the application of Keating's valence force field model to non-ideal wurtzite materials such as GaN, InN and AlN.

We compare continuum and atomistic models for the electromechanical fields in wurtzite GaN/AlN quantum dots and their relative impact on the electronic band structure. Qualitative agreement between atomistic strain calculations and continuum elastic models for a wurtzite hexagonal quantum-dot structure is demonstrated; however, significant quantitative discrepancies of up to 100 meV are observed. A smaller difference of approximately 15 meV is found between fully coupled and semi-coupled continuum models.

The modeling of the vibrational structure of materials is of great help for the use of vibrational spectroscopy for structural characterization. This is especially true in presence of conjugated π electrons where the delocalized nature of π orbitals produces long-range interactions responsible for a marked dependence of the vibrational states on the confinement. This effect is due to the finite size of the molecules as well as to chemical and/or structural defects or to the presence of nanocrystals. To model the vibrational states we adopt a semiempirical model developed in the framework of a tight binding theory for π electrons (Huckel theory). This treatment has been already successfully applied in the past to the study of the vibrational dynamics of polyynes, graphene and carbon nanotubes and it is here extended to the case of sp linear carbon chains (polyynes). It is shown that the effect of the confinement on the vibrational features is influenced by the presence of a Kohn anomaly in the limit of a cumulenic structure. This behaviour is shared by all conjugated carbon materials irrespective of the hybridization of C atoms (sp 2 or sp).

A theoretical approach to the lattice dynamics of Si 1 - x Ge x alloys within a valence force field framework is discussed. A modified Keating model, the anharmonic Keating, was employed to perform supercell calculations in order to investigate accurately the three Raman active optical phonon modes. Theoretical results on both relaxed and strained SiGe samples are shown. A detailed study of the biaxial strain-induced shift of phonon modes of epitaxial SiGe alloys has been performed in all the composition range. Furthermore, a comparison of experimental data with the model results on phonon strain shift coefficients will be also discussed.

Newly synthesized Co(III) complexes of piperazine glyoxime (PGO) are examined from the vibrational spectroscopy point of view. A complete interpretation of the vibrational spectra of both the ligand and the complex has been carried out on the basis of normal coordinate analysis. A valence force field has been developed for both of the compounds. The vibrational spectra of the compounds are simulated by a visual basic program prepared to run on an MS Excel data sheet. (C) 2003 Elsevier B.V. All rights reserved.

Microscopic strain distribution in II–VI–O alloy systems is theoretically analyzed using the valence force field model. ZnSeO and ZnSO alloys have a maximum strain energy at O composition of 50% due to a large lattice mismatch between constituting materials. Zn–Se bond length decreases with increasing O composition and Zn–O bond increases with decreasing O composition. Se atoms rather than O are easier to move in order to reduce strain energy because of the small elastic constant of ZnSe compared with ZnO. The lattice deformation occurs mainly at tetrahedra containing O–Zn–Se bonds with Zn atom in the center.

A model is proposed describing the bond length and bond-bending angle distributions in quaternary A3B5 alloys with ZB structure in quasi-continuum approximation. The model allows to consider reasonably large crystal lattice clusters employing minimum computing resources. Analytical expressions are derived for the radial distribution functions. The developed approach is applied to the analysis of available experimental data on structural disorder in III–V alloys. Employing the valence force field Keating model the deformation energy for several alloys is evaluated.

We have performed an atomic-scale simulation of (100) thin films heteroepitaxial growth of semiconductors with zincblende structure by associating a Monte Carlo technique with an energy model based on the valence force field approximation. It is shown that grooves showing (111) facets are formed in the early stages of the growth owing to enhanced interlayer migrations. The strain relief can be achieved within a few atomic layers, in agreement with experimental observations.

Calcium chloride (40CaCl2 and 44CaCl2) and bromide (40CaBr2) complexes of 4,13-diaza-18-crown-6 (DA-18C6) were investigated using IR and Raman spectroscopy and normal coordinate analysis (NCA). Calcium isotopic substitution was used to determine the valence force field of the DA–18C6–CaCl2 complex (C2h symmetry). Practically no change in the vibrations of the macrocyclic ligand were observed upon complex formation, indicating the absence of conformational distortion.

FT-Raman and FT-IR spectra are reported for 3,3-dimethylglutarimide, its N-deuterated derivative and the Hg(II) complex with 3,3-dimethylglutarimidate ion, Hg(C7H10NO2)2·H2O. A complete vibrational assignments are given for all internal vibrations of the molecules and are supported by normal coordinate analyses based on a general valence force field. The calculated frequencies are in very good agreement with the experiment. The antisymmetric and symmetric Hg–N stretching vibrations are assigned at 562 and 520 cm−1, respectively. It follows that the exocyclic CO bonds in the N-coordinated 3,3-dimethylglutarimidato-Hg(II) complex are more basic that those in free neutral ligand.

We have simulated the growth of GaSb/(00l)GaAs, and we have focused our study on the defects creation at the DA and DB double steps on the substrate. A Monte Carlo scheme associated with a valence force field approximation is used to describe, respectively, the kinetic and the strain effects in the mis-matched film. These simulations indicate a strong localization of dislocation half loops at the step edges in accordance with experimental observations.

The influence of structural size and geometry on the electronic energy levels, impurity binding energies, and absorption characteristics of InAs/GaAs quantum dots grown in the Stranski–Krastanow mode is investigated. Our calculation accounts for the variation in the strain throughout these structures using the valence force field method. A multiband effective mass approach to describing the dot states has been adopted. We predict a strong absorption response in the 1.0–1.1 eV range of energies, in agreement with several recent experiments. Furthermore, the optical spectra are dominated by features arising from transitions between states with the same quantum numbers and transitions between states whose quantum numbers differ by one. Whether a dot exhibits a near-band gap absorption response due to transitions of the latter type depends on the aspect ratio of its base radius and height in a way that can be predicted from a simple particle in a rigid rectangular box model. We have also found that the pyramidal geometry of the dot plays an important role in determining the binding energy of a donor impurity placed at different positions within the dot.

The Raman wavenumbers of bicyclo[2.1.0]pentane (BCP), isolated in a low-temperature matrix, are presented and assignments for all vibrational fundamentals are proposed. The molecular structure of BCP is calculated by means of semi-empirical quantum-mechanics and a normal coordinate analysis of the strained bicyclic system is performed in internal coordinates in terms of a valence force field.

Conformational searches of 1,4-bis(dimethylhydroxysilyl)benzene and 1,4-bis(dimethylhydroxysilyl)-2,3,5,6-tetramethylbenzene were conducted in order to determine the global minimum conformations of these materials. Dimethylsiloxy linkages between phenyl and tetramethylphenyl were also investigated to gain insight into possible differences in properties between polymers based on these two silphenylenes. Searches were performed using InsightII®'s Discover® module and the consistent valence force field. Results for the diphenyl linkage (unhindered system) showed an unexpected global minimum conformation that may help to explain some of the thermal properties previously reported for this crystalline polymer. Results for the di-tetramethylphenyl linkage (hindered system) were consistent with other studies investigating diphenyl linkages, however, the energy contour for this system suggested a higher rotational energy compared to the former system. These results have encouraged us to proceed with the synthesis of the hindered system.

The method of extracting harmonic information from inertial defect differences has been used to obtain sufficient information for a determination of the complete force field for 1,1-difluoroethylene. The presumption that inertial defect differences for non-totally-symmetric vibrations of orthorhombic molecules contain purely harmonic information (1992. D. Christen, J. Mol. Spectrosc. 151, 1-11) must be revoked, however. Copyright 1998 Academic Press. Copyright 1998Academic Press

A normal mode analysis of syndiotactic poly(1-butene) of form I having (TTGG)2 conformation was made in accordance with the valence force field derived by Holland-Moritz for isotactic poly(1-butene) of form I. The assignments were made successfully using polarized infrared and Raman spectra. Based on the assignments, spectral characters in the melt and the low temperature were investigated. The infrared and Raman spectra did not change in the melt but the CCH bendings of the spectra in the low temperature were sensitive to the conformation.

In the early stages of highly mismatched heteroepitaxy (e.g. for InAs deposited on GaAs) self assembled dots (SAD) with a sharp distribution in sizes appear as soon as the coverage exceeds a critical value. We show that this phenomenon is determined by the preliminary growth of 2D platelets which act as precursors for the formation of 3D coherent islands. The argumentation is based on a total energy calculation using a valence force field approach for the elastic part (including dimers), the residual surface contribution (dangling bonds) being added separately. It is demonstrated that the existence of a critical coverage is related to the interaction between platelets. The proposed mechanism provides an appealing explanation for the fairly good calibration of the observed 3D islands. Moreover, our description appears to give the right order of magnitude for the 2D platelets size, the early quantum dots size, the width of the Gaussian distribution, the magnitude of the critical coverage, and finally the fact that such a phenomenon is not observed at lower values of the mismatch.

Monte Carlo technique and Valence force field approximation are used to investigate the heteroepitaxial growth with high lattice mismatch. It is shown that the growing surface becomes rough very rapidly. Its morphology is stabilized and shows V-grooves with (111) facets. The grooves are filled with highly mobile liquid-like atoms that can be incorporated in stable solid-like positions through collective motions and reactions.

The modified general valence force field (GVFF) of the free cyclopentadienyl (Cp) anion was developed with internal coordinates to perform the normal coordinate analysis (NCA). Further it is shown that it is possible to transfer the GVFF of the free ring to the coordinated form. The NCA and the GVFF of (Cp)Tl with inclusion of the ring ligand is presented for the first time. Good agreement between observed and calculated wavenumbers has been achieved for both model calculations, the (Cp)K and the (Cp)Tl. The force fields together with force constants and potential energy distribution are given.

Infrared and Raman spectra of polycrystalline Y2O3 as well as polarized Raman spectra of Y2O3 single crystals have been measured. A complete assignment of the bands is proposed. A normal coordinate analysis using a generalized valence force field enabled us to fit the observed frequencies with a satisfactory accuracy (3.5%). The calculated force constants are discussed and compared with those of α-Al2O3 exhibiting the same atomic coordination.

The molecular structure of bis(dipivaloylmethanato)copper(II) has been determined by sector-microphotometer gas electron diffraction. The experimental data are consistent with a monomeric square-planar structure with ∠OCuO = 93.7 ± 0.7°. The structural parameters are as follows: r g ( CuO ) = 1.916 ± 0.005 A , r g ( CO ) = 1.284 ± 0.009 A , r g ( CC ring ) = 1.399 ± 0.023 A , r g ( CC t ) = 1.581 ± 0.022 A , r g ( C t C m ) = 1.512 ± 0.006 A , r g ( C m H ) = 1.112 ± 0.009 A . The amplitudes of vibration have been calculated by a normal vibration treatment using a valence force field.

A general valence force field is determined from the experimental vibrational frequencies and elastic constants of α-Al 2 O 3 in order to relate the macroscopic elasticity of this material to its microscopic elasticity characterized by the bond-stretching and angle-beading force constants. The evolution of the frequencies, elastic constants, and force field as a function of temperature is discussed.

A zero-order normal coordinate analysis was made for 2,4-difluoronitrobenzene, 2,5-difluoronitrobenzene and 2,5-dibromonitrobenzene, transferring the force constants from our earlier work. The observed and calculated frequencies agree with an average error of 14.7 cm −1 . Unambiguous vibrational assignments of both in-plane and out-of-plane fundamentals of the three molecules have been made and revised assignments are suggested.

Normal coordinate analysis of pyrrole and deuterated pyrroles C 4 H 4 ND, C 4 D 4 NH and C 4 D 4 ND has been performed in a valence force field including simulation of anharmonicity. The change of the form of the vibrations due to deuteration are discussed, and the force field is correlated with results from a molecular orbital calculation.

Normal coordinate analysis of the [Fe(CN)5NO]2− ion in the ground and nearly infinitely long-lived metastable electronic state was performed in valence force field approximation, using our own spectral data. The changes in the molecular parameters in the metastable electronic state are discussed.

Fourier-transform infrared and Raman spectra of l -Ala- l -Ser, d -Ala- l -Ser and l -Ser- l -Ala were recorded, and significant differences were found between the spectra of these dipeptides. In order to interpret these differences, the normal vibrations of l -Ala- l -Ser, d -Ala- l -Ser, l -Ser- l -Ala and d -Ser- l -Ala were calculated from an empirical general valence force field and molecular geometries calculated by MM2 methods. Initial values of the force constants for the normal coordinate analysis were transferred from the known spectroscopic empirical force fields of alanine, serine and poly( l -alanine). Then, a partial refinement of force constants was performed to improve the fit to the experimental spectra of l -Ala, l -Ser and some of their deuterated analogues. Differences were obtained between the calculated spectra of ll and dl derivatives; the significant differences between the experimental spectra, however, could be reproduced with limited success, suggesting that the latter may be due in part to differences in crystal rather than in molecular structures.

A normal coordinate analysis has been performed for H10Si10O15 by applying the modified general valence force field determined for H8Si8O12. Using group theory allows a quantitative correlation of all infrared and Raman active fundamentals of the two molecules, for which the experimental spectra are presented.

The bond lengths for the Ge x Si 1− x alloys are calculated in the empirical tight-binding force model with using a zincblend-like unit cell to simulate the Ge x Si 1− x alloys. The results agree with the experiments quite well, showing that the bond lengths are independent on the alloy composition and close to the Pauling's limit. The failure of the valence force field model in calculating the bond lengths for Ge x Si 1− x alloys is discussed.

Results are presented of an optimized valence force field of the dihydridoosmium(II) complex [(mes)OsH2(CO)] (mesC6H3(CH3) 3-2,4,6) in which the ring was treated as a point mass. The Raman and IR spectra of metal-coordinated mesitylene are given and the results of normal coordinate analysis of the arene described. From the results, a modified general valence force field including the whole ring ligand has been calculated. The results are discussed, and compared with those of the model with point mass approximation.

Using the quasi-isolated molecule approximation, coupled calculations were done of the normal vibrational frequencies and intensities of the IR absorption bands of s- d -glucose. An analysis of the normal vibrational frequencies was done using a valence force field approximation. The intensities were calculated using the CNDO/2 method. A detailed interpretation of the observed IR spectrum is given.

Normal coordinate analysis of propene and five differently deuterated propenes (CH 2 CDCH 3 , CD 2 CHCH 3 , CH 2 CHCD 3 , CH 2 CHCH 2 D, and CD 2 CDCD 3 ) was performed with the valence force field method, using the spectral data obtained by Fourier transform spectroscopy. An internal coordinate basis set and a non-idealized geometry were applied. The changes of the molecular parameters due to adsorption in the zeolite are discussed.

The infrared spectra of seven bis( N -phenyl-substituted hydroxynaphthylaldiminate) complexes of Cu(II) were scanned from 4000 to 100 cm −1 . Particular emphasis is given to the low-energy region. The assignment of the chelate normal modes is supported by an approximate normal coordinate analysis based on a simplified general valence force field, and the geometrical parameters of the bis( N -phenylsalicylaldiminate)Cu(II) complex. The bands near 390 and 285 cm −1 are assigned to the CuO and CuN stretching vibrations, respectively. The corresponding force constants are estimated to be 1.37 and 0.88 mdyn A −1 . Influence of the nature of the different ligands on the structure of complexes is discussed. Similarity of the vibrational spectra for all the complexes suggests that they possess the same type of structure.

We have performed an atomic-scale simulation of lattice-mismatched heteroepitaxial growth of semiconductors with a zincblende structure by associating the Monte Carlo technique with an energy model based on the valence force field approximation. We have observed the formation of misfit dislocations by alignment of point defects. We have evaluated the critical thickness for their creation which are in good agreement with experimental results for high lattice mismatches (greater than 6%), while previous macroscopic models give good results for low lattice mismatches (less than 4%). The deposition of alloy films is investigated to study the variations in the density and the nature of interface defects, leading to misfit dislocations.

From the most precise experimental measurements available from the gas phase for the three vibrational wavenumbers of P 4 , the primary stretching force constant f r = 2.06 mdyn A −1 and two stretch—stretch interaction constants have been evaluated using a simple valence force field. The positive value of f rr 1 and negative value of f rr are confirmed and the value of f r is found to be significantly smaller (15% and 7% respectively) than the corresponding values calculated from the infrared spectra of solutions of phosphorus in carbon disulphide reported in the literature.

A complete interpretation of the benzylidenemethylamine vibrational spectrum has been carried out on the basis of normal coordinate analysis. A valence force field refined on three isotopic species of benzylidenemethylamine has been determined. The obtained force constants have been used to calculate the vibrational spectra of benzylideneaniline (C6H5CHNC6H5) and its fluorosubstituents (4FC6H4NCHC6H5, C6F5 N  CHC6H5, C6H5NCHC6F5 and C6F5NCHC6F5). The normal coordinate analysis has been carried out using the new experimental data from the IR and Raman spectra of the parent molecule, its partially and perdeuterated isotopomers and 15N labelled species of benzylideneaniline [1] and 15N fluorosubstituents [2]. The influence of the substitution of H atoms of the phenyl rings by one F atom on the azomethine group modes has been studied.

A general procedure is described for vibrational analysis, using an ab initio force constant matrix which is transformed into the generalized valence force field. A method using numerical least-square fitting and redundancy elimination is proposed to determine the valence-symmetry coordinates in terms of the internal coordinate displacements. The computer program was customized to simplify the data deck construction and to input most of the data directly from the GAUSSIAN 8X output file.

The valence force field of fluorinated benzenes (in units 106 cm−2) has been created which may be used for calculations and full interpretation of vibrational spectra of more complex polyfluoroaromatic compounds.

Density functional (DF) calculations have been carried out on the in-plane harmonic frequencies and valence force field of benzene. The calculated force constants are in excellent qualitative agreement with previous scaled ab initio forcefields. Harmonic frequencies are predicted with an average deviation of 16.7 cm −1 (1.5%) for the frequencies, not including CH stretching modes. The present study is at variance with a previous DF investigation of Albertazzi and Zerbetto, where the calculated force constant differed considerably from those obtained by scaled ab initio methods.

Raman spectra of sulfur vapor at 620°C under 530.8 nm excitation basically consist of resonance Raman spectra of S4 molecule. Only the three symmetric modes are observed, valence force field calculations confirm the trans planar structure C2h of S4.

A general valence force field for 1-methylthymine (1MeT) in the isolated state has been unequivocally determined from the calculation of both the frequencies and the relative ultraviolet resonance Raman intensities arising from the first lowest lying vibronic transitions. In a second step, the normal modes were derived for the crystalline state using the previously determined in-plane force field and an out-of-plane force field was deduced.

The results of an investigation of the infrared spectra of mono(diethylenetriamine)copper(II) compounds are reported, with particular reference to the low-energy region. Most assignments are based on the available literature. Assignments of the skeletal normal modes are supported by an approximate normal coordinate analysis, taking into account a modified general valence force field to obtain the frequencies and potential energy distribution.

Force constant calculations have been carried out for Ni(PBr3)4 using a simple valence force field with interaction constants. The force constant values are compared for the coordinated and free ligand and also with k(NiP) stretching in the series of molecules Ni(PX3)4 where X=F, Cl, Me. The k(NiP) stretching force constant in Ni(PBr3)4 is much lower than its corresponding values for other members of the series. This is discussed in relation to the observed experimental instability of the compound and the electronegativities of the substituents X in PX3.

2-Methyl-4-trinitromethyl-1,2,3-triazol has been studied by gas-phase electron diffraction. By using the valence force field the mean amplitudes of the vibrations and shrinkage corrections have been calculated. The following geometrical parameters have been obtained assuming C 2v molecular symmetry for a triazol cycle (bond distances r a given in angstroms, angles ∠ α in degrees; standard deviations given in parentheses): NC=1.358(5), NN=1.314(3), NC Me =1.450 fix , N cyc  C=1.444(7), C cyc C cyc =1.385(12) dep , CN=1.528(2), NO=1.201(2), NNN=117.6 fix , NNC=103.0(3), CCC=130.0(9), CCN=109.6(4), CNO=114.9(2), o(C cyc -C)=33.0(20), o(CN)=35.4(40), 68.7(30) and 43.4(30). The positive direction of the torsion angles o corresponds to a clockwise rotation about CC cyc and NC bonds from staggered conformation. These results are compared to the corresponding quantities for some similar molecules.

When a grown crystalline layer is as thin as one or two monolayers, the lattice constant in a grown layer is coherent with the substrate lattice even in a highly lattice-mismatched crystalline system. In this study, we calculate the strain energy in deviated bond lengths and bond angles for individual atoms by valence force field (VFF) method and find the atom position with the minimum strain energy. The critical thickness below which no dislocation occurs is derived. The thickness is thinner as compared with those predicted by previous conventional theories. However, the experimental results agree fairly well with our theoretical results.

Infrared and Raman spectra were obtained for 4,4-dimethyl-2-pentyne. Vibrational assignments were made with the aid of normal coordinate calculations that utilized a 20-parameter modified valence force field, with the values of the force constants being transferred from 4-methyl-2-pentyne. Molecular mechanics calculations were also made in order to calculate the molecular geometry and heat of formation.

Infrared and Raman spectra were obtained for 3-methylbut-1-yne and 3,3-dimethylbut-1-yne. Vibrational assignments were made with the aid of normal coordinate calculations that utilized a 27-parameter modified valence force field. The average difference between the observed and calculated wavenumbers was 6.0 cm −1 for the two molecules. Molecular mechanics calculations were also done for both compounds.