scholarly journals Molecular Dynamics of the Phase Transition in Compressible Ammonium Chloride

1984 ◽  
Vol 37 (6) ◽  
pp. 667
Author(s):  
Sadhana Pandey ◽  
SK Trikha
Keyword(s):  
Phase Transition ◽  
Molecular Dynamics ◽  
Computer Simulation ◽  
High Pressure ◽  
Raman Spectrum ◽  
Ammonium Chloride ◽  
Dynamical Behaviour ◽  
Lennard Jones ◽  
Nearest Neighbours ◽  
Computer Simulation Technique

The effects of pressure on the dynamical behaviour of an NH: ion near the A transition under the influence of its nearest neighbours in ammonium chloride have been studied by using the computer simulation technique. The Lennard Jones (6-12) potential is used as the representative interaction between NH: and Cl-. The present calculations reveal a decrease in entropy of the system with increasing pressure. The libration frequency of the NH: ion is estimated to be approximately 170, 182 and 210 cm -1 at pressures of 1 atm, 3 and 10 kbar respectively, in agreement with the Raman spectrum study of NH4CI at high pressure (Ebisuzaki and Nicol 1969).

scholarly journals Computer Simulation Studies of the Phase Transition in Compressible Deuteroammonium Chloride

1985 ◽  
Vol 38 (5) ◽  
pp. 733
Author(s):  
Sadhana Pandey ◽  
SK Trikha
Keyword(s):  
Phase Transition ◽  
Computer Simulation ◽  
Dynamical Behaviour ◽  
Simulation Technique ◽  
Simulation Studies ◽  
Lennard Jones ◽  
Nearest Neighbours ◽  
Computer Simulation Technique ◽  
Computer Simulation Studies

The effects of pressure on the dynamical behaviour of an ND t ion near the A transition under the influence of its nearest neighbours in deuteroammonium chloride have been studied by using the computer simulation technique. The well-known Lennard Jones (6-12) potential is used as the representative interaction between ND t and CI-. The libration frequency of the ND t ion is estimated to be approximately 130 and 145 cm -1 at pressures of 1 atm and 3 kbar respectively.

scholarly journals Rotational Motion of the NH+4 Ion in Ammonium Chloride

1984 ◽  
Vol 37 (2) ◽  
pp. 197
Author(s):  
Sadhana Pandey ◽  
SK Trikha
Keyword(s):  
Computer Simulation ◽  
Rotational Motion ◽  
Three Dimensional ◽  
Rotational Dynamics ◽  
Ammonium Ion ◽  
Lennard Jones Potential ◽  
Jones Potential ◽  
Lennard Jones ◽  
Nearest Neighbours ◽  
Computer Simulation Technique

The rotational motion of the ammonium ion in NH4CI at low temperature under the influence of its nearest neighbours has been studied using a computer simulation technique. The Lennard Jones potential is used as the representative interaction between NHt and CI-. Three values of the time increment At occurring in the algorithm equation are taken to illustrate the three-dimensional effect on the rotational dynamics of the NH: ion. In each case we notice a well defined transition gap around = 1�25 separating phases II and III which are known from the literature. The libration frequency of the ammonium ion is found to be 1"0; 170 em-1, corresponding to the transition temperature of 242 K, which is in agreement with the Raman spectra study by Couzi et af. (1973).

scholarly journals A variational approach to nucleation simulation

2016 ◽  
Vol 195 ◽  
pp. 557-568 ◽  
Author(s):  
Pablo M. Piaggi ◽  
Omar Valsson ◽  
Michele Parrinello
Keyword(s):  
Molecular Dynamics ◽  
Computer Simulation ◽  
Free Energy ◽  
Variational Approach ◽  
Sampling Method ◽  
Enhanced Sampling ◽  
Technical Problems ◽  
Lennard Jones ◽  
Dynamics Simulations

We study by computer simulation the nucleation of a supersaturated Lennard-Jones vapor into the liquid phase. The large free energy barriers to transition make the time scale of this process impossible to study by ordinary molecular dynamics simulations. Therefore we use a recently developed enhanced sampling method [Valsson and Parrinello, Phys. Rev. Lett.113, 090601 (2014)] based on the variational determination of a bias potential. We differ from previous applications of this method in that the bias is constructed on the basis of the physical model provided by the classical theory of nucleation. We examine the technical problems associated with this approach. Our results are very satisfactory and will pave the way for calculating the nucleation rates in many systems.

COMPARISON BETWEEN MOLECULAR DYNAMICS AND MONTE CARLO DESCRIPTIONS OF SOLID–LIQUID PHASE-TRANSITION OF LENNARD–JONES FLUIDS

2010 ◽  
Vol 21 (03) ◽  
pp. 349-363 ◽  
Author(s):  
A. S. MARTINS ◽  
C. X. S. SEIXAS ◽  
L. B. dos SANTOS ◽  
P. R. RIOS
Keyword(s):  
Phase Transition ◽  
Molecular Dynamics ◽  
Monte Carlo ◽  
Liquid Phase ◽  
Structural Evolution ◽  
Liquid Phase Transition ◽  
Monte Carlo Techniques ◽  
Lennard Jones ◽  
Liquid Transition ◽  
Solid Liquid

Molecular dynamics and Monte Carlo techniques are employed for the study of Lennard–Jones fluids near the solid–liquid transition region. Systematic comparisons between the predictions of both techniques are discussed, with particular emphasis on the structural evolution and location of the transition (melting) temperature Tm.

scholarly journals Effect of Short-range Repulsive Interactions on the Dynamics of the Methane Molecule

1993 ◽  
Vol 46 (2) ◽  
pp. 305
Author(s):  
MK Kansal ◽  
SK Trikha
Keyword(s):  
Short Range ◽  
Torsional Oscillation ◽  
Three Dimensional ◽  
Direction Cosine ◽  
Dynamical Behaviour ◽  
Methane Molecule ◽  
Repulsive Interaction ◽  
Lennard Jones ◽  
Nearest Neighbours ◽  
Before And After

Using a computer simulation technique, an attempt has been made to explain the A-type transition in the specific heat of solid methane at around 20 K in terms of the changes in the dynamical behaviour of the methane molecule under the influence of its nearest neighbours. Different exponents of the short-range repulsive interaction occurring in the expression for the potential energy have been tried in order to select the appropriate value. The well known Lennard-Jones (6-12) and (6-15) potentials are found to reveal a phase transition in a well defined region. From an analysis of the direction cosine data, the three-dimensional motion of the central methane molecule has been visualised before and after the transition. Pertaining to the Lennard-Jones potential, the period of the torsional oscillation (libration) of the methane molecule comes out to be of the order of 0�3xlO-12 s. From the computed critical rotational kinetic. energy, the transition temperature is found to be 20�2 K which agrees well with experimental observations.

Molecular dynamics study of solid nitrogen at high pressure

1981 ◽  
Vol 59 (4) ◽  
pp. 530-534 ◽  
Author(s):  
Michael L. Klein ◽  
D. Levesque ◽  
J.-J. Weis
Keyword(s):  
Molecular Dynamics ◽  
High Pressure ◽  
Room Temperature ◽  
Power Spectra ◽  
Dynamical Behaviour ◽  
Dynamical Structure ◽  
Structure And Dynamics ◽  
Solid Nitrogen ◽  
Rotational Motions ◽  
Real Solid

A molecular dynamics study has been carried out of the structure and dynamics of solid nitrogen in its high pressure, room temperature, plastic crystal phase: cubic Pm3n. We employed a system of 512 molecules interacting via atom–atom potentials. As in the real solid our simulated crystal is composed of two types of molecules whose dynamical behaviour is quite distinct. We present calculations of the power spectra associated with translational and rotational motions as well as the phonon response embodied in the dynamical structure factor S(Q, ω).

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