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Simulating Fluid Phase Equilibria from First Principles

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Simulating Fluid Phase Equilibria from First Principles

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  1. Virtual Laboratory for Earth and Planetary Materials, VLabRenata Wenztcovitch, Yousef Saad, Ilja Siepmann, Don Truhlar, Dave Yuen (Minnesota), Philip Allen (Stony Brook), Gordon Erlebacher (Florida), Bijaya Karki (Louisiana), Marlon Pierce (Indiana), Frank Spera (Santa Barbara),ITR 0428774, 0425059, 0427264, 0426601, 0426867, 0426757 Simulating Fluid Phase Equilibria from First Principles Phase diagrams play a central role in thermodynamics and water holds a unique role among fluids, not only because of its ubiquity and importance on Earth, but more so because of its anomalous liquid properties. This work presents the first calculation of the vapor-liquid coexistence curve for water using a first principles representation and efficient Monte Carlo algorithms. The BLYP density functional representation yields a saturated liquid density and normal boiling and critical temperatures which are somewhat underestimated. M.J. McGrath, J.I. Siepmann, I-F.W. Kuo, C.J. Mundy, J. VandeVondele J. Hutter, F. Mohamed, and M. Krack,Simulating Fluid Phase Equilibria of Water from First Principles , in press, J. Phys. Chem. A 2005, in press (Truhlar Festschrift). Computer resources were provided by LLNL and MSI Colored according to molecular dipole 3.2 D < purple < 3.3 D1.8 D < red < 1.9 D http://vlab.msi.umn.edu

  2. Virtual Laboratory for Earth and Planetary Materials, VLabRenata Wenztcovitch, Yousef Saad, Ilja Siepmann, Don Truhlar, Dave Yuen (Minnesota), Philip Allen (Stony Brook), Gordon Erlebacher (Florida), Bijaya Karki (Louisiana), Marlon Pierce (Indiana), Frank Spera (Santa Barbara),ITR 0428774, 0425059, 0427264, 0426601, 0426867, 0426757 Improved Density Functionals for Water The ubiquitous nature of water has prompted great interest in using simulation techniques, such as molecular dynamics and Monte Carlo methods, to better understand the structure and properties of liquid water and ice. Recent attention has focused on using density functional theory (DFT) as a means to study these systems, however the high expense of these simulations has restricted the choice of available density functionals to less costly, and often, less accurate, methods. We have compared a series of 25 density functional methods to highly accurate ab initio “data” for a set of 28 water dimers and 8 water trimers, in order to assess the accuracy of existing density functional methods. Furthermore, we have gone on to optimize a new functional, PBE1W, that achieves accuracy equal to that of the best existing (and more costly DFT methods) while retaining the cost-effectiveness of those methods currently in use. Dahlke, E. E.; Truhlar, D. G.,Improved density functionals for water, J. Phys. Chem. B, in press (2005). The newly parameterized density functionals (purple) perform better than those currently in use in solid state simulation (yellow and green) and as well as, or better than, the more expensive functionals commonly used in quantum chemistry (blue, red, and grey). All errors in the figure are relative to binding energies obtained using the Weizmann-1 level of theory. http://vlab.msi.umn.edu

  3. Virtual Laboratory for Earth and Planetary Materials, VLabRenata Wenztcovitch, Yousef Saad, Ilja Siepmann, Don Truhlar, Dave Yuen (Minnesota), Philip Allen (Stony Brook), Gordon Erlebacher (Florida), Bijaya Karki (Louisiana), Marlon Pierce (Indiana), Frank Spera (Santa Barbara),ITR 0428774, 0425059, 0427264, 0426601, 0426867, 0426757 Low ↔ High Density Transformations in H2O Ice Structural change upon compression (upper figures) of low density ice, consisting of a single hydrogen-bond network, into high density ice, consisting of two interpenetrating hydrogen-bond networks. The opposite is observed under decompression (lower figures). Ice XI and VIII are prototypical forms of low- and high-density ice. We observed direct reconstructions between these phases in both directions. These transformations are not observed in practice, instead both phases amorphize. From this perspective, the amorphous can be viewed as an intermediate step in the low  high density transformations. The reconstruction paths we observed bypass the intermediate amorphous phases and preserve the style of dipole ordering of the parent structure leading to metastable phases and large hystereses. Umemoto, K., Wentzcovitch, R., Theoretical reinvestigation of the isostructural transformation in ice VIII, Phys. Rev. B 71, 012102 (2005). Umemoto, K., Wentzcovitch, R., Low  high density transformations in ice, Chem. Phys. Lett. 405, 59 (2005). http://vlab.msi.umn.edu

  4. Virtual Laboratory for Earth and Planetary Materials, VLabRenata Wenztcovitch, Yousef Saad, Ilja Siepmann, Don Truhlar, Dave Yuen (Minnesota), Philip Allen (Stony Brook), Gordon Erlebacher (Florida), Bijaya Karki (Louisiana), Marlon Pierce (Indiana), Frank Spera (Santa Barbara),ITR 0428774, 0425059, 0427264, 0426601, 0426867, 0426757 Thermal-Chemical Convection Simulations Including Materials Properties Obtained by First Principles Today it is possible to model thermal-chemical convection and mantle dynamics taking into account thermodynamics and rheological properties of multi-phase aggregates. First principles calculations are nowadays offering input for these simulations that cannot be obtained by other means. Particularly important is the knowledge of phase boundaries and changes in properties resulting from phase transitions. Contrast in properties across the post-perovskite transition in the deep mantle computed by first principles by Tsuchiya et al., were used to perform novel simulations. This transition appears to inhibit the formation of superplumes unless some form of radiative heat transport is included in these simulations. Matyska , C. and Yuen,D.A.,The importance of radiative heat transfer on superplumes in the lower mantle with the new post-perovskite phase change, Earth Planet. Sci. Lett. 234, 72 (2005). Comparison between two-dimensional upwelling developments for constant thermal conductivity (top panel) and for radiative thermal conductivity (bottom panel) in thermal-chemical convection including both, the post-spinel transition in the transition zone, and the post-perovskite transition above the core mantle boundary. http://vlab.msi.umn.edu

  5. Virtual Laboratory for Earth and Planetary Materials, VLabRenata Wenztcovitch, Yousef Saad, Ilja Siepmann, Don Truhlar, Dave Yuen (Minnesota), Philip Allen (Stony Brook), Gordon Erlebacher (Florida), Bijaya Karki (Louisiana), Marlon Pierce (Indiana), Frank Spera (Santa Barbara),ITR 0428774, 0425059, 0427264, 0426601, 0426867, 0426757 Automatic Workflow for First PrinciplesEquations of State Generation Obtaining equation of state or elasticity from first principles (FP) at finite temperatures is a time consuming procedure that involves hundreds of job submissions and runs. Results from some runs must be used as parameters in the subsequent ones. Input preparation from run to run is usually made by the user. However, data manipulation between runs are well defined and decisions to be made during execution of the workflow are also easily predictable. This permits these workflows to be programmed and scheduled for automatic execution. We designed an algorithm necessary to run automatically workflows for equation of state computation. Human involvement is restricted to the elaboration of a single initial input, which is not much more complex than the typical input for a single execution of an FP code. The present implementation makes extensive use of awk, shell scripting, and auxiliary C programs. The usual workflow was restructured to achieve high degree of parallelism and is well suited for implementation in distributed environments. da Silva, C. R. S.,Automatic Workflow for First Principles Equations of State Generation. Block diagram for automatic generation of equations of state. Action blocks embody high degree of parallelism. http//:vlab.msi.umn.edu

  6. Virtual Laboratory for Earth and Planetary Materials, VLabRenata Wenztcovitch, Yousef Saad, Ilja Siepmann, Don Truhlar, Dave Yuen (Minnesota), Philip Allen (Stony Brook), Gordon Erlebacher (Florida), Bijaya Karki (Louisiana), Marlon Pierce (Indiana), Frank Spera (Santa Barbara),ITR 0428774 Automatic Workflow for First PrinciplesEquations of State Generation Most repetitive work is due to parameter space sampling (pressure, strains, phonon q-points). For efficiency sake structures are usually optimized in increasing order of pressures (output Pn-1  input Pn ). This implies in sequential runs. Solution: Generate an approximate Equation of State (EOS), VxP  Acceptable initial configuration at any pressure is available  Calculations at various pressures is decoupled and can run in parallel. Other parameters sampling (strains, q-points) are naturally parallelizable. da Silva, C. R. S., Automatic workflow for first principles equations of state generation. Flow diagram for the action blocks labeled “Long Refine” and “Lagrangean Strains” in previous page. http://vlab.msi.umn.edu

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