X-Message-Number: 16151 From: "Jan Coetzee" <> Subject: =?iso-8859-1?Q?Phase_In=2C_Phase_Out_-_With_a_Little_Help_From_Your_PC!_?= Date: Sat, 28 Apr 2001 19:40:30 -0400 This is a multi-part message in MIME format. ------=_NextPart_000_002C_01C0D01B.1587F560 Content-Type: text/plain; charset="iso-8859-1" The thought of determining phase diagrams has traditionally sparked fear in to the hearts of scientists, meaning long hours at the bench coupled with complex calculations. But now, thanks to Equilibria, the latest module in MSI's (soon to become Accelrys) Materials Studio PC-based modelling software, hard-worked and time-starved researchers can take off their white coats and leave the bench, down their calculators and grab the nearest mouse. Equilibria enables users to easily simulate phase diagrams on the PC, releasing valuable time for additional research or instead go to the beach! Michael Francis tells us more... What exactly are phase diagrams and why are they so important? Phase diagrams are a graphical visualisation of the state of a material as a function of temperature, pressure and concentrations of the constituent components and give an understanding of solubility and phase coexistence. As a result they are vitally important in many fields - alloy design, petrochemicals, the packaging industry (in particular foodstuffs), adhesives, detergents, and pharmaceuticals to name a few. Their experimental determination becomes more difficult as the number of components increases, and involves the extrapolation of thermodynamic functions followed by further refinement, all of which, as expected, are hungry on time and resources. To further complicate matters, both the interaction energies and free energies are required to calculate solubilities - a challenging and tricky limitation [1]. In order to address these difficulties, any technique must be able to sample the configuration space of the molecules efficiently and work in conjunction with a forcefield that can work over a wide range of temperatures and pressures and also handle simultaneously both the vapor and condensed phases. "Phase diagrams for many important components are difficult to determine. Good experimental data require expensive equipment and weeks of measurements" explains Dr Gerhard Goldbeck-Wood, Director of the MSI's Polymer Consortium. "Critical points for a number of systems such as long chain hydrocarbons are out of the reach of experimental methods. Empirical methods for mixtures tend to perform poorly for mixtures of small and long molecules. Direct simulations offer an attractive alternative in these difficult cases". Equilibria Equilbria, a completely new software product within the Materials Studio environment and over a year in development, addresses all these challenges. Using the Gibbs Ensemble Monte Carlo method [2] a state-of-the-art technology to simulate chemical potential equilibrium between two phases, Equilibria offers a comprehensive set of simulation tools to determine the phase equilibria of hydrocarbon molecules and their binary and ternary mixtures, and is the first direct simulation product for phase diagrams. Such simulations provide thermodynamic data, which assist materials research and process design in the chemicals and petrochemicals industries. "Phase coexistence simulations have been developed and tested in academia for a number of years. Equilibria brings this state-of-the-art technology to the desktop of the industrial chemist and chemical engineer" adds Goldbeck-Wood. "Equilibria is the first commercial software tool which allows the industrial chemist and chemical engineer to determine phase coexistence data by simulation alone. Its full integration into the Materials Studio modeling environment ensures the ease of use of this technology and its accessibility from the desktop." So how does Equilibria work? So how does Equilibria work? The Gibbs Ensemble method used enables the direct simulation of vapor-liquid and liquid-liquid phase coexistence properties of single components and mixtures from a single. These methods allow the determination of the phase coexistence even for larger alkanes (e.g. C48), and solubilities to be determined of alkanes and a-alkenes in poly(olefins). From the vapor-liquid equilibrium data, Equilibria determines critical constants. The software provides a tool to determine the second virial coefficient of single components. Equilibria is supported by the NERD [3] united atom forcefield, so named from the initials of its developers, which is carefully parameterised and allows the effect on phase coexistence of even small variations in molecular structure to be determined with confidence. This forcefield covers all linear and branched saturated alkanes, a-alkenes and nitrogen. The parameter files are open enabling the user to edit the parameters and even extend the range to other groups, e.g. higher alkenes. ------=_NextPart_000_002C_01C0D01B.1587F560 Content-Type: text/html; [ AUTOMATICALLY SKIPPING HTML ENCODING! ] Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=16151