Potential Energy Calculations Research Articles

A new calculation of potential energy of supporting springs and the application in design of vibrating ring gyroscope

High-performance micro-gyroscopes are needed in many applications, including inertial navigation, control, and defense/avionics/space. The ring gyroscope provides a number of advantages, including excellent mode matching, high-resolution; low zero-rate output, and long-term stability. In order to get more accurate drive/control/sense policy and to improve the performance of vibrating ring gyroscope (VRG), potential energy of the semi-circular cantilever supporting spring in VRG is expressed as the function of general coordinates; By calculating the partial differentials of the potential energy the disturbing items, actual stiffness, coupling stiffness of VRG are obtained; Resonant frequency and frequency splitting of the sensing modes of VRG are obtained from the actual stiffness and coupling stiffness. The method presented in this paper is suitable to get the above key parameters of the VRG both with ideal symmetrical structure and structure of fabrication errors. Complex mechanical and material principles are avoided and the compact analytical calculation is presented in detail in this paper. The conclusions and simulations in this paper will be used in developing the drive/control/sensing policy of high-performance VRG lately.

Mapping the mesospheric CO 2 clouds on Mars: MEx/OMEGA and MEx/HRSC observations and challenges for atmospheric models

This study presents the latest results on the mesospheric CO 2 clouds in the martian atmosphere based on observations by OMEGA and HRSC onboard Mars Express. We have mapped the mesospheric CO 2 clouds during nearly three martian years of OMEGA data yielding a cloud dataset of ∼60 occurrences. The global mapping shows that the equatorial clouds are mainly observed in a distinct longitudinal corridor, at seasons L s = 0–60° and again at and after L s = 90°. A recent observation shows that the equatorial CO 2 cloud season may start as early as at L s = 330°. Three cases of mesospheric midlatitude autumn clouds have been observed. Two cloud shadow observations enabled the mapping of the cloud optical depth ( τ = 0.01–0.6 with median values of 0.13–0.2 at λ = 1 μm) and the effective radii (mainly 1–3 μm with median values of 2.0–2.3 μm) of the cloud crystals. The HRSC dataset of 28 high-altitude cloud observations shows that the observed clouds reside mainly in the altitude range ∼60–85 km and their east–west speeds range from 15 to 107 m/s. Two clouds at southern midlatitudes were observed at an altitude range of 53–62 km. The speed of one of these southern midlatitude clouds was measured, and it exhibited west–east oriented speeds between 5 and 42 m/s. The seasonal and geographical distribution as well as the observed altitudes are mostly in line with previous work. The LMD Mars Global Climate Model shows that at the cloud altitude range (65–85 km) the temperatures exhibit significant daily variability (caused by the thermal tides) with the coldest temperatures towards the end of the afternoon. The GCM predicts the coldest temperatures of this altitude range and the season L s = 0–30° in the longitudinal corridor where most of the cloud observations have been made. However, the model does not predict supersaturation, but the GCM-predicted winds are in fair agreement with the HRSC-measured cloud speeds. The clouds exhibit variable morphologies, but mainly cirrus-type, filamented clouds are observed (nearly all HRSC observations and most of OMEGA observations). In ∼15% of OMEGA observations, clumpy, round cloud structures are observed, but very few clouds in the HRSC dataset show similar morphology. These observations of clumpy, cumuliform-type clouds raise questions on the possibility of mesospheric convection on Mars, and we discuss this hypothesis based on Convective Available Potential Energy calculations.

Redetermination of 5α-androstane-3,17-dione.

The structure of the title compound, C19H28O2, has been redermined at 295 (2) K, with much improved precision. The structure and mol­ecular packing of the title compound was first reported by Coiro et al. [Acta Cryst. (1973). B29, 1404–1409] by means of potential-energy calculations. The cell parameters in this study differ considerably in space group C2. It is a derivative of testosterone and consists of a cyclo­penta­none ring (A) fused to to successive cyclo­hexane (B and C) and cyclo­hexa­none (D) rings. The three cyclo­hexa­none rings are in slightly distorted boat configurations and the cyclo­penta­none ring is a distorted half-chair. The crystal packing is stabilized by weak inter­molecular C—H⋯O inter­actions involving O atoms from each of the cyclo­hexa­none and cyclo­penta­none rings and H atoms from each of their respective rings.

Study on the Dispersion of Nano-Sized Bismuth Powders in Octane Solvent

Abstract Three types of fatty acids—oleic acid, stearic acid, and 12-hydroxystearic acid—were used to disperse nano-sized bismuth powders in octane solvents. The surface characteristics of bismuth powders were modified to be hydrophobic in nature, and the bismuth-fatty acid formed on the surface. Stability property of the suspension was measured by ultraviolet-visible spectrophotometer. Results indicate that better suspension stabilization can be achieved when the 12-hydroxystearic acid is used. Adsorption behavior reveals that a greater affinity at the solid/liquid interface occurred for the 12-hydroxystearic acid than that for stearic acid or oleic acid. This observation suggests that the adsorption of 12-hydroxystearic acid may lead to a better packing of the acid molecules onto the solid surface than others and also results in better suspension stability. It is also evidenced by the results of theoretical calculation of potential energies that the colloidal stability of organic bismuth suspension is caused by fatty acid reducing the attractive interparticle potential and by steric repulsion mechanism.

Fluorene-based oligomers as red light-emitting materials: a density functional theory study

The electronic structures, charge injection and transport, absorption and emission spectra, properties of two series of fluorene-based oligomers {2-[2-{2-[5-(9H-Fluoren-3-yl)-thiophen-2-yl]-vinyl}-6-(2-thiophen-2-yl-vinyl)-pyran- 4-ylidene]-malononitrile} n (FTPM) n and {2-{2-{2-[5-(9H-Fluoren-2-yl)-2-hydroxy- 3-methoxy-phenyl]-vinyl}-6-[2-(2-hydroxy-3-methoxy-phenyl)-vinyl]-pyran-4- ylidene}-malononitrile} n (FOOPM) n (n = 1–4) have been investigated by the density functional theory (DFT) approach. The ground-state geometries of (FTPM)4 and (FOOPM)4 optimized at B3LYP/6-31G(d) level exhibited zigzag arrangements. The energies of HOMO and LUMO, HOMO–LUMO energy gaps (ΔE H–L) of (FTPM) n and (FOOPM) n (n = ∞) were obtained by linear extrapolation method. Moreover, the calculations of ionization potential (IP), electronic affinity (EA), and reorganization energy (λ) were used to evaluate the charge injection and transport abilities. For (FTPM)4 and (FOOPM)4, the TDDFT calculations revealed that the absorption peaks can be characterized as π–π* transition and couple with the location of electron density distribution changes in different repeat units. All the earlier theoretical investigations are intended to establish the structure–property relationships, which can provide guidance to design the organic light-emitting diodes (OLEDs) with high performance.

Vortex core switching by coherent excitation controlled by defect in nanodisk

We have studied vortex core switching in a Permalloy disk with a cavity defect using micromagnetic simulation and analytical calculation methods. It is demonstrated that the existence of a cavity that can attract and pin the vortex core in the nanodisk plays an important role in controlling the reversal of the vortex core by coherent excitation. The diagram of the vortex core switching with different cavity radii is presented based on the calculation of the effective potential energy. It is shown that there are three cases that are dependent on the distance between the cavity and the disk centers. For a smaller distance, the reversal cannot occur without applying a second sufficiently strong field pulse with the direction opposite to the orientation of the first pulse, and the amplitude of the second field pulse that can release and reverse the polarity of the vortex core increases with increasing of the radius of the cavity. Then, for a critical distance range, the vortex core can be released from the cavity and reverse automatically. When the distance is large enough the vortex core cannot be attracted and pinned by the cavity, the reversal cannot be controlled by the cavity.

Molecular mechanics and all-electron fragment molecular orbital calculations on mutated polyglutamine peptides

We perform potential energy calculations on mutant polyglutamine peptides that were studied experimentally, and found to aggregate with varying efficiencies. Low-energy structures were generated for each peptide by simulated annealing molecular dynamics, and were analyzed by molecular mechanics and by all-electron fragment molecular orbital energy calculations. In order to make a comparison between the two sets of potential energies, we devised a means of computing molecular-mechanical analogues of the quantum-mechanical energies. Our results suggest that in accordance with a previous paper (VanSchouwen et al., submitted for publication [16]) the experimentally-observed inhibition of aggregation is due to localized, geometry-based effects on peptide structure, with little appreciable perturbation from longer-range non-bonded effects.

Investigation of the interaction of some astrobiological molecules with the surface of a graphite (0 0 0 1) substrate. Application to the CO, HCN, H 2O and H 2CO molecules

Detailed interaction potential energy calculations are performed to determine the potential energy surface experienced by the molecules CO, HCN, H 2O and H 2CO, when adsorbed on the basal plane (0 0 0 1) of graphite at low temperatures. The potential energy surface is used to find the equilibrium site and configuration of a molecule on the surface and its corresponding adsorption energy. The diffusion constant associated with molecular surface diffusion is calculated for each molecule.

A new approach for long range corrections in molecular dynamics simulation with application to calculation of argon properties

In the application of long range corrections to calculation of potential energy and pressure utilizing molecular dynamics simulation, it is common to use a longer distance of cut-off to obtain more accurate results. The radial distribution function is assumed to be equal to unity in conventional terms for the long range corrections. The main objective of this work is to introduce a methodology for obtaining a correlation for radial distribution function from preliminary simulation runs and then use it in other simulation runs with a smaller ratio of cut-off distance to collision diameter. This, in turn, results in much lower CPU time requirements. The radial distribution function is considered as a convergent oscillating function. A number of simulations were performed in NVT ensemble with the ratio of cut-off distance to collision diameter set to five. Also, two sets of simulations with the ratio of two were performed. The first set used the conventional term of long range corrections and the second used the term presented in this work. With the ratio of two, calculating the pressure of argon in liquid and supercritical fluid states resulted in much lower CPU time and less error. In predicting pressure, applying the new correlation for radial distribution function reduced the CPU time by a factor of twelve. Assuming cut-off distance to be twice the collision diameter also resulted in a decrease of nearly 4% in relative error. In addition, the effect of this modification on argon properties: such as heat capacity, thermal pressure coefficient and isothermal compressibility are investigated using molecular dynamics simulation data in fluctuation formulas.

Line-on-Line Organic−Organic Heteroepitaxy of Quaterrylene on Hexa-peri-hexabenzocoronene on Au(111)

In a recent paper, we discussed the optical properties of a heterostructure consisting of a highly ordered monolayer of quaterrylene (QT), electronically decoupled from the gold substrate by a predeposited epitaxial monolayer of hexa-peri-hexabenzocoronene (HBC). Here we now present the detailed structural investigation of this organic double-layer system. We show that the structure of the heterosystem can be identified as line-on-line coincidence (lol), a new type of epitaxy discovered by us previously for the system 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on HBC on highly oriented pyrolytic graphite (HOPG). Additionally, we provide evidence on the basis of advanced potential energy calculations that indeed energetic gain drives this lol growth mode.

Excited state intramolecular proton transfer in 3-hydroxy flavone and 5-hydroxy flavone: A DFT based comparative study

Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of 3-hydroxy-flavone (3HF) and 5-hydroxy-flavone (5HF) were studied using DFT/B3LYP (6-31G (d,p)) and TD-DFT/B3LYP (6-31G (d,p)) level of theory respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer for both the compounds. Calculated PE curves of 3HF for the ground and excited singlet states proton transfer process explain its four state laser diagram. Excited states PE calculations support the ESIPT process to both 5HF and 3HF. The difference in ESIPT emission process of 3HF and 5HF have been explained in terms of HOMO and LUMO electron distribution of the enol and keto tautomer of these two compounds.

Monolayer Solids of Short Alkanes and Perfluoroalkanes

Potential energy calculations are used to discuss the relative stability of monolayer solid latices on graphite for C2H6, C3H8, C2F6, and C3F8. Triangular, centered-rectangular, and herringbone lattices are treated. The calculations use all-atom models and are based on nonbonding interactions formulated for three-dimensional dense phases of alkanes and perfluoroalkanes. Experimental adsorption energies are used to discriminate among several proposed models.

Potential energy calculations for various water dimer configurations

Intermolecular potential energy curves are presented and analyzed for three different water dimer structures: the normal hydrogen-bonded structure (Cs); a weakly hydrogen-bonded structure (C1) thought to be important in encounters of hydrated ions in aqueous solution; and a repulsive configuration (C2h) characterized by a head-on approach of hydrogen atoms (OH … HO). Results are based on ab initio calculations [SCF and CI (at the MP2 level), with and without counterpoise (CP) correction for basis set superposition error (BSSE)] and also a recent semiempirical effective pair potential (RWK2). The CP corrections have a significant effect on the location and depth of the potential wells for the hydrogen-bonded structures, even when CI and extended basis sets are employed.

Surfactant and Electrolyte Effects on Latex Depletion Flocculation by Thickeners

AbstractSummary: Polymer thickeners can induce good dispersion, bridging, or depletion flocculation of latexes depending on the polymer structure and concentration. Unlike non‐associative polymers, associative polymers have the ability to create a good latex dispersion. However, when the associative interactions are destroyed, depletion flocculation of the latex can result. This happens when an excess of ionic surfactant is added to the system. In addition, the surfactant may associate with the thickener backbone, thus modifying the molecular volume of the polymer thickener. This paper explores the effect of anionic surfactant and electrolyte on the molecular volume of both associative and non‐associative thickeners. Both HEUR and HASE structures are included. For HEUR thickeners, formation of a pseudo‐polyelectrolyte through the association of anionic surfactant with the polyethylene oxide backbone is confirmed. Further, the ability of the thickener to depletion flocculate latexes as a function of surfactant and electrolyte is explored. Experimental critical flocculation concentrations (CFC) are compared to values expected based on molecular volume and potential energy calculations. A good correlation is found between molecular volume and CFC for a wide range of thickener compositions.

Stereochemistry and Electronic structure of anticonvulsant drugs

Anticonvulsant drugs come from a range of chemical types, but most drugs show important structural features in common. It has been suggested elsewhere that molecular conformation may be an important factor in determining activity. The present work has been designed to investigate the influence of both stereochemistry and electronic structure on anticonvulsant action. Empirical potential energy calculations are first used to determine preferred conformations. It is found that anticonvulsants adopt a common preferred conformation, which is likely to be responsible for anticonvulsant activity. Molecular electrostatic potentials are also calculated for anticonvulsants, after first being evaluated in a series of model compounds. Electrostatic potentials based on MINDO/3 wave functions are found to be well suited to molecules containing carbonyl groups, and are also able to provide a quantitative estimate of reactivity. Applications to anticonvulsants shows the existence of a common electrostatic field, where similar regions of positive and negative potential are seen throughout the series studied. The structure-activity relationship outlined here applies to anticonvulsant activity against experimental electroshock seizures, and associated clinical use in the treatment of tonic-clonic (grand mal) epilepsy. It appears that both stereochemical and electronic factors play an important role in determining the activity of anticonvulsant drugs.

Conformational energy calculations on the CNS-active peptide Pro-Leu-Gly-NH2

Partitioned potential energy calculations, inclusive of hydrogen bond potential function, were performed on the molecular conformations of the endocrine- and extraendocrine-active tripeptide H-Pro-Leu-Gly-NH2. A complete search for energetically stable structures revealed the presence of type Iβ and IIβ turn conformations, with the latter being the preferred conformation. Results of cndo/2 molecular orbital calculations were found to be in consonance with the partitioned potential energy calculations. These data are in agreement with earlier nuclear magnetic resonance and crystallographic studies.

Base displacement in AAF and AF modified dCpdG: syn and anti Guanine

Minimized conformational potential-energy calculations have been performed for the major adduct of N-2-acetylaminofluorene (AAF) and aminofluorene (AF) with dCpdG. The DNA backbone conformations that produce base displacement, about which no information was previously available, were ascertained. For the AAF adduct, five different combinations of the DNA backbone torsions ..omega..', ..omega.., and psi produce low-energy conformers in which the fluorene is coplanar with cytidine, and the guanine is syn and twisted nearly perpendicular to the AAF. For the deacetylated AF adduct, three additional backbone types yielded fluorene-cytidine stacked conformers. In these conformers the guanine was anti. The various modes of achieving base-displacement may occur under differing circumstances, such as extent of modification, base sequence, salt concentration, and the nature of the adduct (acetylated or deacetylated).

Fibrous structures: Their character and the role of interatomic forces in their analysis

An introduction is given to the various types of spatial relationships that occur among molecules in fibrous materials and the concepts associated with their diffraction. Fibrous materials provide limited diffraction patterns that rarely contain enough information to completely determine the atomic arrangement in the fiber repeat unit. This information must be supplemented with chemical and physical information to uniquely characterize the structure. The analysis of the diffraction from the polysaccharide heparin is presented in detail to illustrate how calculations of the nonbonded interatomic potential energy were used as a criterion for developing a model of the structure. The model is sterically reasonable and is consistent with the diffraction pattern.

X-ray and DFT Study of Glaucocalyxin A Compound with Cytotoxic Activity

The title compound glaucocalyxin A (1) (7, 14-dihydroxy-ent-kaur-16-en-3,15-dione) isolated from the leaves of isodon excisoides was characterized by IR, 1H NMR, 13C NMR, 1H-1H COSY, HMQC, HMBC, and EIMS, and its crystal structure was determined by single-crystal X-ray diffraction. The X-ray crystal structure revealed that the molecular backbone of the chosen crystal is a tetracyclic system, including three six-membered rings and a five-membered ring, and the three six-membered rings are in a chair-like conformation. The five-membered ring adopts a twisted envelope-like conformation, and its geometrical parameters were compared with theoretical calculations at the B3LYP and HF level of theory. The molecules form extensive networks through the intra- and intermolecular hydrogen bonds. The experimental NMR data were interpreted with the aid of magnetic shielding constant calculations, by means of the GIAO (gauge-lncluding atomic orbitals) method. Calculated and experimental results were compared with a satisfactory level of agreement. Molecular electrostatic potential map was used in an attempt to identify key features of the diterpenoid glaucocalyxin A that is necessary for its activity. Calculations of molecular electrostatic potential and stabilization energies suggest that the protonation of glaucocalyxin A will be able to occur on carbonyl oxygen atoms.

Determining the internal rotations of p-thiocresol

This Letter presents findings about the very low barriers hindering the internal rotations of p-thiocresol from microwave spectroscopy and ab initio calculations. The rotational spectrum of p-thiocresol has been studied using a Balle–Flygare type Fourier-transform microwave spectrometer. The assignment of the transitions allows the determination of rotational constants, centrifugal distortion constants, and the potential barrier hindering the internal rotations. Second-order Møller–Plesset perturbation theory (MP2) in connection with high-level basis sets has been used for the theoretical calculation of potential energies during the torsions of the functional groups and the determination of their equilibrium positions.