摘要:

Monte Carlo (MC) simulations were performed for systems of hard oblate spherocylinders with breadth-to-height ratios φ = 0.5–3.5 and packing fractionsy= 0.25–0.45 and for Kihara oblate molecule systems of φ = 1 at reduced temperaturesT*= 0.75 and 1.0 andy= 0.05–0.45. The compression factors and the dependence of the average correlation functions on the shortest surface-to-surface distance were determined for the case of hard oblate spherocylinders and the compression factors, residual internal energies and average correlation functions for the case of the generalized Kihara molecule systems. In addition, values of the third virial coefficient of the hard oblate spherocylinders were evaluated in the range of φ = 1–3. Results of the MC simulations for the hard oblate spherocylinders compare well with the available data in the literature and theoretical values; thermodynamic functions of the Kihara molecule systems were determined from the second-order perturbation theory. They agree well with our MC values at lower densities and higher reduced temperatures.

ISSN:0026-8976    

DOI:10.1080/00268970009483313

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Accurate values have been obtained for the electric dipole(μ)and quadrupole(Θ)moment and the dipole polarizability (ααβ) of CS, SiO and SiS from finite-field many-body perturbation theory and coupled cluster calculations. For the ground state of the dipole moment we have obtainedμ/ea0= 0.7903 (CS), −1.1843 (SiO) and −0.6124 (SiS) and for the quadrupole moment Θ/ea20= −1.85 (CS), −2.94 (SiO) and −0.37 (SiS). These values agree well with the available experimental data for the dipole moment. Discrepancies between theory and experiment are observed for the quadrupole moment of CS, SiO and SiS. Our best values for the mean dipole polarizability of the isoelectronic CS and SiO are= 28.87 (CS) and 29.67 (SiO). SiO is less anisotropic than CS, as Δα/e2a20E−1h= 14.45 (CS) and 7.66 (SiO). The dipole and quadrupole moments, the mean and the anisotropy of the polarizability of SiS at the MP4 level of theory vary around the equilibrium bond lengthReaswith

ISSN:0026-8976    

DOI:10.1080/00268970009483314

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Indirect membrane-mediated forces influence aggregation, segregation and freezing processes of large particles inserted into a membrane or adsorbed to its surface. Colloidal particles, polymers, peptides and proteins are the source of deformations of the lipid double layer. These perturbations cause membrane-mediated attractive or repulsive forces between the particles. A molecular statistical treatment is useful for investigating the lateral organization of peripheral and trans-membrane peptides. To describe aggregation and freezing phenomena a density functional, which includes conventional short-range forces and membrane-mediated effects, is proposed. The method is applied to an ensemble of adsorbed peptides. It is investigated how the elastic splay-distortion modulus, the surface tension, the compression-expansion modulus of the bilayer and the cross-section of adsorbed particles influence aggregation and freezing. Assuming conventional values for the material parameters, membrane-mediated attractive forces are found to be sufficiently strong to enforce aggregation.

ISSN:0026-8976    

DOI:10.1080/00268970009483315

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The 2v3overtone band of six different isotopomers of cyanogen bromide has been recorded in the range from 4200 to 4400 cm−1with a resolution of 0.02 cm−1using a Fourier transform infrared (FTIR) spectrometer. This allowed us to achieve complete knowledge of the energies for all levels corresponding to double vibrational excitation. An improved evaluation of the quartic force field of cyanogen bromide has been performed using the new data obtained together with those already known from previous works. Theoretical values derived from a recentab initiocalculation have been used to constrain the potential terms which cannot be determined with sufficient precision by the least-squares analysis of the available experimental data.

ISSN:0026-8976    

DOI:10.1080/00268970009483316

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The behaviour of the harmonic infrared frequency of diatomic molecules subjected to moderate static uniform electric fields is analysed. The potential energy expression has been developed as a function of a static uniform electric field, which brings about a formulation describing the frequency versus field strength curve. With the help of the first and second derivatives of the expressions obtained, which correspond to the first- and second-order Stark effects, it was possible to find the maxima of the frequency versus field strength curves for a series of molecules using a Newton-Raphson search. A method is proposed which requires only the calculation of a few energy derivatives at a particular value of the field strength. At the same time, the expression for the dependence of the interatomic distance on the electric field strength is derived and the minimum of this curve is found for the same species. Derived expressions and numerical results are discussed and compared with other studies.

ISSN:0026-8976    

DOI:10.1080/00268970009483317

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A canonical molecular dynamics (MD) simulation was accelerated by using an efficient implementation of the multiple timestep integrator algorithm combined with the periodic fast multiple method (MEFMM) for both Coulombic and van der Waals interactions. Although a significant reduction in computational cost has been obtained previously by using the integrated method, in which the MEFMM was used only to calculate Coulombic interactions (Kawata, M., and Mikami, M., 2000, 98,J. Comput. Chem., in press), the extension of this method to include van der Waals interactions yielded further acceleration of the overall MD calculation by a factor of about two. Compared with conventional methods, such as the velocity-Verlet algorithm combined with the Ewald method (timestep of 0.25 fs), the speedup by using the extended integrated method amounted to a factor of 500 for a 100 ps simulation. Therefore, the extended method reduces substantially the computational effort of large scale MD simulations.

ISSN:0026-8976    

DOI:10.1080/00268970009483318

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The dispersion coefficients C6, C8and C10for the interactions between helium and helium-like ions in the metastable states of 21S and 23S with Z up to 10 are calculated using variational wave functions in Hylleraas coordinates.

ISSN:0026-8976    

DOI:10.1080/00268970009483319

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We present the equations and methodology for the theoretical prediction of the conductance, permeability and selectivity of a K+channel on the basis of atomic scale models for it. The methodology involves the use of Langevin dynamics and activated trajectories in order to obtain translocation free energies, rate constants and transmission coefficients for an ion going through the channel. The models are for the Inward Rectifier K+channel (IRK1) which is a member of a family of ion-selective K+channels. The IRK1 channel is biologically important because of its role in cardiac pacemaker function. The models we use for the IRK1 channel are developed from a model of the Shaker voltage-gated K+channel. We find that the theoretically predicted conductance is too low by three orders of magnitude. We attribute this underestimate to a specific structural defect in the model used. Perhaps our most significant result is that the computed conductance is tremendously sensitive to the structural details of the so-called ‘P-loop’ that lines the outer half of the permeation pathway of the channel. This sensitivity may be useful in future studies on ion channel proteins for which the structure is not known from X-ray crystallography. In addition, this sensitivity may help determine whether X-ray structures of these proteins correspond to open or closed conformations.

ISSN:0026-8976    

DOI:10.1080/00268970009483320

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor