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  • 1
    Electronic Resource
    Electronic Resource
    6-Azasteroids: Structure-Activity Relationships for Inhibition of Type 1 and 2 Human 5.alpha.-Reductase and Human Adrenal 3.beta.-Hydroxy-.DELTA.5-steroid Dehydrogenase/3-Keto-.DELTA.5-steroid Isomerase (1994)
    s.l. : American Chemical Society
    Journal of medicinal chemistry 37 (1994), S. 2352-2360 
    Details
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jm00041a014
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  • 2
    Electronic Resource
    Electronic Resource
    Pulsed laser melting of silicon: A molecular dynamics study (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2336-2339 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the results of a molecular dynamics study of the pulsed laser melting of crystalline silicon. The Stillinger–Weber potential is employed for the atomic interaction. A 23 ps laser pulse of 0.2 J/cm2 is assumed to deliver 9×1013 W/g to the crystal. The energy is delivered at a constant rate over the 23 ps time interval. For the first 14 ps the temperature increases in a linear manner as functions of time. At 14 ps the crystal reaches the limit of superheating and melts over the next 4 ps interval of time. We discuss various quantities as functions of time: temperature, density, energies, and structure factors. An upper limit of 1750 K is determined for melting temperature and a value of 932 J/g for the latent heat, compared to the experimental values 1683 K and 1800 J/g, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453703
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular dynamic calculation of elastic constants of silicon (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 4028-4031 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Stillinger and Weber have introduced a model potential to study the solid and liquid forms of silicon. This potential has been used in a number of computer simulation studies of silicon. We have calculated the elastic constants of silicon using the Stillinger–Weber potential at three different temperatures T=888, 1164, and 1477 K. The adiabatic elastic constants are calculated using fluctuation formula appropriate for the microcanonical ensemble. We find that the calculated shear modulus C44 is smaller than the experimental values by ∼30% at T=888 K, ∼40% at the two higher temperatures, and the modulus C12 is larger than the experimental value by 25%–30%. Simulations with N=216 and 1728 particles were carried out to check on the number dependence of the results. These two particle numbers give equivalent results for the elastic constants. The calculated elastic constants show the same softening with rising temperature as shown by the experimental values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450871
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  • 4
    Electronic Resource
    Electronic Resource
    Free energy difference calculations comparing fcc and hcp structures using molecular dynamics computer simulations (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 1795-1802 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamic computer simulation methods have been employed to calculate the free energy difference between the fcc and hcp structures using a Morse potential parametrized to model Ni. The calculation is carried out for a temperature (∼1000 K) where anharmonic effects are important and also for a range of interactions about each particle. In addition, at the same temperature, another calculation using only nearest neighbor interactions was performed. Using lattice sums the potential energy for the two static lattices was calculated. For the Morse potential used, static lattice sums give a lower potential for the hcp structure. With only nearest neighbor interactions, the fcc–hcp free energy difference is determined only by the entropy difference. In this case the fcc structure has the lower free energy. When both anharmonic effects and longer range interactions are considered we find, at the temperature and density investigated, that the hcp structure is more stable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450426
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  • 5
    Electronic Resource
    Electronic Resource
    Statistical ensembles and molecular dynamics studies of anisotropic solids. II (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4243-4247 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have recently discussed how the Parrinello–Rahman theory can be brought into accord with the theory of the elastic and thermodynamic behavior of anisotropic media. This involves the isoenthalpic–isotension ensemble of statistical mechanics. Nosé has developed a canonical ensemble form of molecular dynamics. We combine Nosé's ideas with the Parrinello–Rahman theory to obtain a canonical form of molecular dynamics appropriate to the study of anisotropic media subjected to arbitrary external stress. We employ this isothermal–isotension ensemble in a study of a fcc→ close-packed structural phase transformation in a Lennard-Jones solid subjected to uniaxial compression. Our interpretation of the Nosé theory does not involve a scaling of the time variable. This latter fact leads to simplifications when studying the time dependence of quantities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448813
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  • 6
    Electronic Resource
    Electronic Resource
    Monte Carlo simulations at constant chemical potential and pressure (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2263-2267 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The usual way of carrying out Monte Carlo simulations of open systems is by using the grand canonical ensemble. In the grand canonical (TVμ) ensemble a system of fixed volume V is in contact with a temperature reservoir having temperature T, and a particle reservoir having chemical potential μ. In order to obtain values for thermodynamic functions for a given pressure in TVμ Monte Carlo simulations a series of simulations at fixed T and V and different chemical potentials is carried out to determine P(μ), and then an extrapolation to the desired pressure must be carried out. Here we discuss Monte Carlo simulations of open systems in the RPμ ensemble in which an energy R, the chemical potential μ, and the pressure are held fixed during the simulation. Thus each RPμ ensemble simulation replaces a set of TVμ simulations. Simulations of an embedded atom model of liquid palladium are discussed using the new method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464207
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  • 7
    Electronic Resource
    Electronic Resource
    Interface response function for a model of sodium: A molecular dynamics study (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 7520-7530 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics studies of the liquid epitaxial crystallization and melting of a model of sodium have been carried out to determine the (001) velocity vs interface temperature and to investigate the microscopic growth and melting mechanisms. The growth involves the correlated growth of at least seven planes. We discuss two independent ways of determining the velocity of growth and melting from the simulation data. Details of how the interface temperature is determined and the variation of the system energy with time in both crystallization and melting are included. The maximum growth velocity is 150 m/s and occurs at approximately one-half the melting temperature. The system continues to crystallize to the lowest temperature investigated (81 K) and the growth is not diffusion limited. If conventional transition state theory is used to describe the simulation data then there is a slope discontinuity at the melting temperature with the melting velocities being much higher than predicted. The average structure factors of planes buried in the crystal vs temperature show similar discontinuities near the melting point and suggests that the higher melting velocities are associated with anharmonic softening.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458188
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  • 8
    Electronic Resource
    Electronic Resource
    Fourth adiabatic ensemble (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 4296-4298 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The statistical mechanics of a new adiabatic ensemble, which allows volume and particle fluctuations, is presented. Characteristic fluctuation formulas and suitable response functions are derived.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458710
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  • 9
    Electronic Resource
    Electronic Resource
    Low temperature phase transformation in superionic conductors: A molecular dynamics study of silver sulfide (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6580-6586 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Upon lowering the temperature below 450 K the superionic solid Ag2 S undergoes a structural phase transformation from a bcc sulfur lattice with the space group Im3m to a monoclinic lattice with the space group P21 /c. We have successfully modeled this transformation using the variable size–shape form of molecular dynamics and a pair potential constructed earlier to model structural and transport properties in the superionic phase. Very good agreement is found between the partial pair distribution functions for the transformed crystal and the distribution functions calculated using the atomic positions obtained in x-ray studies. We also find good agreement between the three-body angular distributions calculated for the transformed system and distributions calculated for the structure based on the x-ray positions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456325
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  • 10
    Electronic Resource
    Electronic Resource
    Including spin in the Raychaudhuri equation (1991)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 485-487 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The Raychaudhuri equation for a spin fluid matter content is developed. The equation is applied to the behavior of an irrotational, unaccelerated fluid. The development of singularities in the expansion is studied for constant spin densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.529439
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