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  • 1
    Electronic Resource
    Electronic Resource
    Chain length and density dependence of the chemical potential of lattice polymers (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 6666-6673 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The chemical potential of lattice polymers is calculated in two alternative ways: by the Widom insertion method using the Rosenbluth and Rosenbluth sampling technique and by the modified Widom method, based on the insertion of one segment to an existing polymer chain. In the first part of this paper we present a detailed derivation of the modified Widom technique for lattice systems. We then proceed to calculate the chemical potential for chains of up to 50-mers in monomeric and polymeric solvents. We observe marked odd-even effects on the chemical potential. The density dependence of the chemical potential is found to vary with chain length. For most temperatures and densities studied the chemical potential of chain molecules in a fixed environment becomes linear in chain length for molecules longer than 10–20 segments. The results are compared to the classical lattice theories, which are found to be best at high densities, as expected based on previous investigations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463671
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  • 2
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of folding transitions of simple model proteins using a chain growth algorithm (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 8644-8652 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed Monte Carlo simulations of folding transitions of model proteins on a simple cubic lattice with the Rosenbluth and Rosenbluth (1955) chain growth algorithm combined with Boltzmann weighting and multilink additions. We use a model proposed by Dill (1985) that represents the protein as a connected sequence of hydrophobic and hydrophilic beads on the lattice, with nearest-neighbor interactions between the constituent beads. The algorithm allows the calculation of equilibrium folding curves for arbitrary sequences of chain lengths of at least 48 in three dimensions. This is significantly longer than the maximum chain length for which equilibrium curves can be determined with the Metropolis (1953) based algorithms used in previous work. The thermal denaturation curve for the model is found to vary greatly with the sequence used, in some special cases approximating closely the sharpness observed for real proteins. These special sequences appear to be simple, periodic arrangements of beads. However, it seems that the unique or almost unique lowest energy states that exist for certain sequences of moderate length approaching the length of the simplest real proteins cannot be recovered in feasible simulation times with our particular model/algorithm combination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463383
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  • 3
    Electronic Resource
    Electronic Resource
    Monte Carlo simulation of the collapse-coil transition in homopolymers (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 6802-6808 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed Monte Carlo simulations of the transition of polymers from an expanded to a collapsed state on a cubic lattice using a variation of the scanning technique of Meirovitch. The technique allows the study of highly compact polymer conformations that could not be studied with previously available methods. Our results indicate that the universal scaling function α3(1−T/θ)n1/2 vs (1−T/θ)n1/2 has a pronounced maximum before leveling off in the fully collapsed regime. Available experimental data for this function only cover the range up to and including the maximum. Good agreement is obtained between our calculations and experimental data for the polystyrene/cyclohexane system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463633
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of sequence and intermolecular interactions on the number and nature of low-energy states for simple model proteins (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3185-3190 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have studied the thermodynamically significant low-energy conformations of 200 random 24-residue model proteins on a square lattice with the Rosenbluth and Rosenbluth (1955) chain growth algorithm combined with multilink additions and Boltzmann weighting. We use a model proposed by Dill (1985) that represents the protein as a connected sequence of hydrophobic and hydrophilic beads on the lattice with nearest-neighbor interactions between the constituent beads. Two interaction sets were investigated—attraction between just the hydrophobic beads and attraction between hydrophobic residues and also between hydrophilic residues. The distribution of energies found with attraction only between hydrophobic beads is broad and consistent with the previous results of Lau and Dill (1989). However, the low-energy states are highly degenerate and noncompact. When attraction between hydrophilic beads is included with the attraction between hydrophobic beads, the energy distribution is sharp. Also, the low-energy configurations are reasonably nondegenerate and compact. This indicates that even with this simple model, important characteristics of the low-energy states of the model proteins are sensitive to the details of the interaction set used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464091
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  • 5
    Electronic Resource
    Electronic Resource
    Phase diagrams of nonideal fluid mixtures from Monte Carlo simulation (1986)
    s.l. : American Chemical Society
    Industrial and engineering chemistry 25 (1986), S. 525-535 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/i100024a012
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  • 6
    Electronic Resource
    Electronic Resource
    Phase diagram of the two-dimensional Coulomb gas: A thermodynamic scaling Monte Carlo study (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 7205-7209 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this work, we report results for the phase diagram of the two-dimensional Coulomb system. We use a recently proposed simulation method, thermodynamic scaling Monte Carlo, to determine the Kosterlitz–Thouless insulator/conductor transition line and the first-order vapor–liquid coexistence curve. The Kosterlitz–Thouless line terminates at the first-order coexistence curve close to the gas–liquid critical point. Our estimate of the vapor–liquid critical point is, T*≈0.056, ρ*≈0.21, in only modest agreement with previous theoretical estimates and semiquantitative numerical results. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471406
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  • 7
    Electronic Resource
    Electronic Resource
    Phase equilibria of a lattice model for an oil–water–amphiphile mixture (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 3718-3725 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monte Carlo simulation and quasichemical theory are used to study the phase behavior of a lattice model for oil–water–amphiphile ternary systems. Several short amphiphiles with varying tail and head lengths are studied. Two- and three-phase coexistence regions are observed as well as the formation of microemulsions. In contrast to previous work on this model, quantitative phase diagrams are determined for both symmetric and asymmetric amphiphiles. The removal and regrowth of whole chains by configurational bias methods is used to help equilibration and sampling. Near quantitative agreement is found between quasichemical theory and our simulations except when one of the phases self-assembles or in the vicinity of a critical point. In these areas the quasichemical theory is still qualitatively correct. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471026
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  • 8
    Electronic Resource
    Electronic Resource
    Monte Carlo simulations of phase equilibria for a lattice homopolymer model (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 1014-1023 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vapor–liquid phase equilibria for lattice homopolymer systems are simulated in the Gibbs ensemble for chains of length n=1, 8, 16, 32, 64, and 128 using a newly proposed methodology for volume change moves [Mackie et al., Europhys. Lett. 27, 549 (1994)]. This is the first time that extensions of the Gibbs ensemble methodology for direct calculation of phase coexistence are presented for lattice models. The simulation results show, in agreement with experiment, that the chain length dependence of the critical temperature of polymer-hole systems follows the Schultz–Flory form. The critical densities obey an n−0.32 scaling relationship over this limited range in chain lengths, an exponent somewhat less than is found from experimental data. We show that both the Flory model and the Guggenheim theory do not agree with the simulation results, although the Guggenheim model permits better agreement in all cases. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469450
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  • 9
    Electronic Resource
    Electronic Resource
    Free energy and phase equilibria for the restricted primitive model of ionic fluids from Monte Carlo simulations (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1452-1459 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this work, we investigate the liquid–vapor phase transition of the restricted primitive model of ionic fluids. We show that at the low temperatures where the phase transition occurs, the system cannot be studied by conventional molecular simulation methods because convergence to equilibrium is slow. To accelerate convergence, we propose cluster Monte Carlo moves capable of moving more than one particle at a time. We then address the issue of charged particle transfers in grand canonical and Gibbs ensemble Monte Carlo simulations, for which we propose a biased particle insertion/destruction scheme capable of sampling short interparticle distances. We compute the chemical potential for the restricted primitive model as a function of temperature and density from grand canonical Monte Carlo simulations and the phase envelope from Gibbs Monte Carlo simulations. Our calculated phase coexistence curve is in agreement with recent results of Caillol obtained on the four-dimensional hypersphere and our own earlier Gibbs ensemble simulations with single-ion transfers, with the exception of the critical temperature, which is lower in the current calculations. Our best estimates for the critical parameters are T*c=0.053, ρ*c=0.025. We conclude with possible future applications of the biased techniques developed here for phase equilibrium calculations for ionic fluids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467770
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  • 10
    Electronic Resource
    Electronic Resource
    High-pressure phase equilibria in ternary systems of propionic acid and water with ethane, sulfur hexafluoride or refrigerant 13 (chlorotrifluoromethane), 23 (trifluoromethane), or 116 (hexafluoroethane) (1991)
    s.l. : American Chemical Society
    Journal of chemical & engineering data 36 (1991), S. 290-293 
    Details
    ISSN: 1520-5134
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/je00003a010
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