1,721,482 research outputs found
First-order nematic-smectic phase transition for hard spherocylinders in the limit of infinite aspect ratio
No full textWe report Monte Carlo simulations of the nematic-smectic phase transition for a system of hard spherocylinders with infinite length-to-diameter ratio. A finite-size scaling analysis suggests that this system undergoes a first-order phase transition. When combined with other simulations of the phase behavior of spherocylinders, these results suggest that the nematic-smectic phase transition is first-order for all aspect ratios. This appears to rule out the possibility of a tricritical point predicted by several density-functional theories.PT: J; CR: BLADON P, 1996, J PHYS-CONDENS MAT, V8, P9445 BOLHUIS P, 1997, J CHEM PHYS, V106, P666 DOGIC Z, 1997, PHYS REV LETT, V78, P2417 FRENKEL D, 1988, J PHYS CHEM-US, V92, P3280 FRENKEL D, 1988, NATURE, V332, P882 HOSINO M, 1979, J PHYS SOC JPN, V46, P1709 MCGROTHER SC, 1996, J CHEM PHYS, V104, P6755 ONSAGER L, 1949, ANN NY ACAD SCI, V51, P627 PONIEWIERSKI A, 1990, PHYS REV A, V41, P6871 PONIEWIERSKI A, 1991, PHYS REV A, V43, P6837 PONIEWIERSKI A, 1992, PHYS REV A, V45, P5605 SOMOZA AM, 1990, PHYS REV A, V41, P965 TENWOLDE PR, 1996, J CHEM PHYS, V104, P9932 TKACHENKO AV, 1996, PHYS REV LETT, V77, P4218 TORRIE GM, 1974, CHEM PHYS LETT, V28, P578 VANDERSCHOOT P, 1996, J PHYS II, V6, P1557 VEERMAN JAC, 1990, PHYS REV A, V41, P3237; NR: 17; TC: 15; J9: PHYS REV E; PG: 4; GA: YM237Source type: Electronic(1
Numerical prediction of the melting curve of n-octane
No full textWe compute the melting curve of n-octane using Molecular Dynamics simulations with a realistic all-atom molecular model. Thermodynamic integration methods are used to calculate the free energy of the system in both the crystalline solid and isotropic liquid phases. The Gibbs-Duhem integration procedure is used to calculate the melting curve, starting with an initial point obtained from the free energy calculations. The calculations yield quantitatively accurate results: in the pressure range of 0-100 MPa, the calculated melting curve deviates by only 3 K from the experimental curve. This deviation falls just within the range of uncertainty of the calculations. (C) 1999 American Institute of Physics. [S0021-9606(99)52128-4].PT: J; CR: ANDERSEN HC, 1983, J COMPUT PHYS, V52, P24 BAEZ LA, 1995, MOL PHYS, V86, P385 BOLHUIS P, 1997, J CHEM PHYS, V106, P666 BOLHUIS PG, 1997, NATURE, V388, P235 CHEN B, 1998, J PHYS CHEM B, V102, P2578 FRENKEL D, 1984, J CHEM PHYS, V81, P3188 FRENKEL D, 1984, PHYS REV LETT, V52, P287 FRENKEL D, 1985, MOL PHYS, V55, P1171 FRENKEL D, 1992, J PHYS-CONDENS MAT, V4, P3053 HABENSCHUSS A, 1989, J CHEM PHYS, V91, P4299 KOFKE DA, 1993, J CHEM PHYS, V98, P4149 KOFKE DA, 1993, MOL PHYS, V78, P1331 KUCHTA B, 1992, PHYS REV B, V45, P5072 KUCHTA B, 1993, PHYS REV B, V47, P14691 KUCHTA B, 1995, J CHEM PHYS, V102, P3349 KUCHTA B, 1997, J CHEM PHYS, V106, P6771 LASO M, 1992, J CHEM PHYS, V97, P2817 MALANOSKI AP, 1997, J CHEM PHYS, V107, P6899 MALANOSKI AP, 1999, J CHEM PHYS, V110, P664 MARTIN MG, 1998, J PHYS CHEM B, V102, P2569 MARTYNA GJ, 1994, J CHEM PHYS, V101, P4177 MARTYNA GJ, 1996, MOL PHYS, V87, P1117 MATHISEN H, 1967, ACTA CHEM SCAND, V21, P9 MEIJER EJ, 1990, J CHEM PHYS, V92, P7570 MOOIJ GCA, 1992, J PHYS CONDENS MATT, V4, L255 NORMAN N, 1961, ACTA CHEM SCAND, V15, P1755 PANAGIOTOPOULOS AZ, 1987, MOL PHYS, V61, P813 PANAGIOTOPOULOS AZ, 1988, MOL PHYS, V63, P527 POLSON JM, UNPUB POLSON JM, 1998, J CHEM PHYS, V109, P318 RYCKAERT JP, 1977, J COMPUT PHYS, V23, P327 RYCKAERT JP, 1985, MOL PHYS, V55, P549 RYCKAERT JP, 1989, MOL PHYS, V67, P957 SCOTT RA, 1966, J CHEM PHYS, V44, P3054 SIEPMANN JI, 1990, MOL PHYS, V70, P1145 SIEPMANN JI, 1992, MOL PHYS, V75, P59 SIEPMANN JI, 1993, NATURE, V365, P330 SINGER SJ, 1990, J CHEM PHYS, V93, P1278 SMIT B, 1989, MOL PHYS, V68, P931 SMIT B, 1995, J CHEM PHYS, V102, P2126 SMITH GD, 1996, J PHYS CHEM-US, V100, P18718 SMITH JC, 1992, J AM CHEM SOC, V114, P801 TOBIAS DJ, 1997, J CHIM PHYS PCB, V94, P1482 TOXVAERD S, 1990, J CHEM PHYS, V93, P4290 TOXVAERD S, 1997, J CHEM PHYS, V107, P5197 TUCKERMAN M, 1992, J CHEM PHYS, V97, P1990 TUCKERMAN ME, 1990, J CHEM PHYS, V93, P1287 VEERMAN JAC, 1990, PHYS REV A, V41, P3237 VEGA C, 1992, J CHEM PHYS, V96, P9060 VEGA C, 1992, J CHEM PHYS, V97, P8543 WATANABE M, 1993, J CHEM PHYS, V99, P8063 WIDOM B, 1963, J CHEM PHYS, V39, P2808 WIDOM B, 1982, J PHYS CHEM-US, V86, P869 WILLIAMS DE, 1967, J CHEM PHYS, V47, P4680 WURFLINGER A, 1975, BER BUNSEN PHYS CHEM, V79, P1195; NR: 55; TC: 30; J9: J CHEM PHYS; PG: 10; GA: 215QQSource type: Electronic(1
Calculation of solid-fluid phase equilibria for systems of chain molecules
No full textWe study the first order solid-fluid phase transition of a system of semi-flexible Lennard-Jones chains using molecular dynamics simulations. Thermodynamic integration methods are used to calculate the free energy of the solid and fluid phases. The solid phase free energy per chain can be calculated to an accuracy of +/-0.03k(B)T with relative ease. The Gibbs-Duhem integration technique is used to trace out the complete melting curve, scarring with a single point on the curve obtained from the foe energy calculations. For the short chains studied here, we find that increasing the chain length stabilizes the solid phase; i.e., it raises the melting temperature at fixed pressure, and lowers the density at the transition at fixed temperature. Gibbs-Duhem integration was used also to investigate the effects of chain stiffness on the transition. We find that increasing the stiffness also acts to stabilize the solid phase. At fixed temperature, the transition is shifted to lower pressure and lower density with increasing chain stiffness. Further, we find that the density gap between solid and fluid broadens with increasing chain stiffness. (C) 1998 American Institute of Physics. [S0021-9606(98)50825-2].PT: J; CR: ANDERSEN HC, 1980, J CHEM PHYS, V72, P2384 BAEZ LA, 1995, MOL PHYS, V86, P385 BERENDSEN HJC, 1984, J CHEM PHYS, V81, P3684 BRUCE AD, 1997, PHYS REV LETT, V79, P3002 BULHUIS PG, 1997, J CHEM PHYS, V106, P666 BULHUIS PG, 1997, NATURE, V388, P235 ESCOBEDO FA, 1997, J CHEM PHYS, V106, P9858 FRENKEL D, 1984, J CHEM PHYS, V81, P3188 FRENKEL D, 1984, PHYS REV LETT, V52, P287 FRENKEL D, 1985, MOL PHYS, V55, P1171 FRENKEL D, 1991, J PHYS-CONDENS MAT, V3, P3053 FYNEWEVER H, 1998, J CHEM PHYS, V108, P1636 HOOVER WG, 1967, J CHEM PHYS, V47, P4873 HOOVER WG, 1985, PHYS REV A, V31, P1695 KOFKE DA, 1993, J CHEM PHYS, V98, P4149 KOFKE DA, 1993, MOL PHYS, V78, P1331 KUCHTA B, 1992, PHYS REV B, V45, P5072 KUCHTA B, 1993, PHYS REV B, V47, P14691 KUCHTA B, 1995, J CHEM PHYS, V102, P3349 KUCHTA B, 1997, J CHEM PHYS, V106, P6771 MARTYNA GJ, 1992, J CHEM PHYS, V97, P2635 MARTYNA GJ, 1996, MOL PHYS, V87, P1117 MEIJER EJ, 1990, J CHEM PHYS, V92, P7570 MOOIJ GCA, 1992, J PHYS CONDENS MATT, V4, L255 NOSE S, 1984, J CHEM PHYS, V81, P511 NOSE S, 1984, MOL PHYS, V52, P255 OGURA H, 1977, PROG THEOR PHYS, V58, P419 PANAGIOTOPOULOS AZ, 1987, MOL PHYS, V61, P813 PARRINELLO M, 1980, PHYS REV LETT, V45, P1196 ROSENBLUTH MN, 1955, J CHEM PHYS, V23, P356 SHENG YJ, 1994, MACROMOLECULES, V27, P400 SHENG YJ, 1996, MACROMOLECULES, V29, P4444 TUCKERMAN M, 1992, J CHEM PHYS, V97, P1990 TUCKERMAN ME, 1990, J CHEM PHYS, V93, P1287 VEERMAN JAC, 1990, PHYS REV A, V41, P3237 WIDOM B, 1963, J CHEM PHYS, V39, P2808 WIDOM B, 1982, J PHYS CHEM-US, V86, P869 WILSON MR, 1993, MOL PHYS, V80, P277 WILSON MR, 1994, MOL PHYS, V81, P675; NR: 39; TC: 26; J9: J CHEM PHYS; PG: 11; GA: 108FLSource type: Electronic(1
Finite-size corrections to the free energies of crystalline solids
No full textWe analyze the finite-size corrections to the free energy of crystals with a fixed center of mass. When we explicitly correct for the leading (ln N/N) corrections, the remaining free energy is found to depend linearly on 1/N. Extrapolating to the thermodynamic limit (N → ∞), we estimate the free energy of a defect-free crystal of particles interacting through an r–12 potential. We also estimate the free energy of perfect hard-sphere crystal near coexistence: at ρσ3 = 1.0409, the excess free energy of a defect-free hard-sphere crystal is 5.918 89(4)kT per particle. This, however, is not the free energy of an equilibrium hard-sphere crystal. The presence of a finite concentration of vacancies results in a reduction of the free energy that is some two orders of magnitude larger than the present error estimate
Ab initio molecular dynamics simulation of laser melting of silicon
No full textThe method of ab initio molecular dynamics, based on finite temperature density functional theory, is used to simulate laser heating of crystal silicon. We have found that a high concentration of excited electrons dramatically weakens the covalent bond. As a result, the system undergoes a melting transition to a metallic state. In contrast to ordinary liquid silicon, the new liquid is characterized by a high coordination number and a strong reduction of covalent bonding effects
Structural, dynamical, electronic, and bonding properties of laser-heated silicon: An ab initio molecular-dynamics study
No full textThe method of ab initio molecular dynamics, based on finite-temperature density-functional theory, is used to simulate laser heating of crystalline silicon. We found that a high concentration of excited electrons dramatically weakens the covalent bonding. As a result the system undergoes a melting transition to a metallic state. We studied several structural, dynamical, electronic, and bonding properties of this phase of silicon. In contrast to ordinary liquid silicon, this liquid is characterized by a high coordination number and a strong reduction of covalent-bonding effects. However this phase is transient. In fact, by strongly reducing the level of electronic excitation, liquid silicon reverts very rapidly to its usual properties
Nonmetal-metal transition in metal–molten-salt solutions
No full textThe method of ab initio molecular dynamics, based on finite-temperature density-functional theory, is used to study the nonmetal-metal transition in two different metal–molten-salt solutions, Kx(KCl)1-x and Nax(NaBr)1-x. As the excess metal concentration is increased the electronic density becomes delocalized and percolating conducting paths are formed, making a significant dc electrical conductivity possible. This marks the onset of the metallic regime. By calculating several electronic and structural properties, remarkable differences between the two solutions are observed. The anomalous behavior of Nax(NaBr)1-x, typical of all the Na-NaX solutions, is found to be related to the strong attractive interaction between the sodium ions and the excess electrons
Hot electrons and the approach to metallic behavior in Kx(KCl)1-x
No full textThe approach to the metallic phase of molten Kx(KCl)1-x mixtures is studied using ab initio molecular dynamics based on finite-temperature density functional theory. The finite electronic temperature is found to result in new and unexpected effects. In particular, we observe a thermally induced lowering of the predicted DC conductivity, which greatly improves the agreement with the experiment, and a widening of the HOMO-LUMO energy gap. We expect that these are genuinely new physical effects which could be observed also in other systems
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