Pedro R. C. da Silveira

Metadata management for distributed first principles calculations in VLab-A collaborative cyberinfrastructure for materials computation

Abstract This paper describes the metadata and metadata management algorithms necessary to handle the concurrent execution of multiple tasks from a single workflow, in a collaborative service oriented architecture environment. Metadata requirements are imposed by the distributed workflow that calculates thermoelastic properties of materials at high pressures and temperatures. The scientific relevance of this workflow is also discussed. We explain the basic metaphor, the receipt, underlying the metadata management. We show the actual java representation of the receipt, and explain how it is converted to XML in order to be transferred between servers, and stored in a database. We also discuss how the collaborative aspect of user activity on running workflows could potentially lead to race conditions, how this affects requirements on metadata, and how these race conditions are precluded. Finally we describe an additional metadata structure, complementary to the receipts, that contains general information about the workflow.

Accurate thermoelastic tensor and acoustic velocities of NaCl

Despite the importance of thermoelastic properties of minerals in geology and geophysics, their measurement at high pressures and temperatures are still challenging. Thus, ab initio calculations are an essential tool for predicting these properties at extreme conditions. Owing to the approximate description of the exchange-correlation energy, approximations used in calculations of vibrational effects, and numerical/methodological approximations, these methods produce systematic deviations. Hybrid schemes combining experimental data and theoretical results have emerged as a way to reconcile available information and offer more reliable predictions at experimentally inaccessible thermodynamics conditions. Here we introduce a method to improve the calculated thermoelastic tensor by using highly accurate thermal equation of state (EoS). The corrective scheme is general, applicable to crystalline solids with any symmetry, and can produce accurate results at conditions where experimental data may not exist. We apply it to rock-salt-type NaCl, a material whose structural properties have been challenging to describe accurately by standard ab initio methods and whose acoustic/seismic properties are important for the gas and oil industry.

Ab initio elasticity workflow in the VLab science gateway

This paper describes a scientific workflow for ab initio calculations of elastic coefficients (Cij) of crystalline materials implemented in the VLab Cyberinfrastructure [da Silveira et al., 2008]. This workflow has recently been upgraded to treat crystals of all symmetries and integrated in the XSEDE. First we review the underlying Cij calculations and list explicitly different requirements for each Bravais lattice. We also describe the workflow management and its general method for handling actions. We illustrate the Cij application with a calculation of diamonds elastic coefficients at high pressures. We conclude with an outlook of future implementation plans.