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Molecular Simulation, Vol. 31, No. 5, April 2005, 297­301 …

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Molecular Simulation, Vol. 31, No. 5, April 2005, 297­301




         Grid computing and molecular simulations: the vision
                      of the eMinerals project
                                                M. T. DOVE.,* and N.H. DE LEEUW§*

                         Department of Earth Sciences University of Cambridge Downing Street Cambridge CB2 3EQ UK
National Institute for Environmental eScience, Centre for Mathematical Sciences University of Cambridge Wilberforce Road Cambridge CB3 0EW UK
                               §School of Crystallography, Birkbeck College Malet Street London WC1E 7HX UK


                                            (Received November 2004; in final form November 2004)


     This paper discusses a number of aspects of using grid computing methods in support of molecular simulations, with
     examples drawn from the eMinerals project. A number of components for a useful grid infrastructure are discussed, including
     the integration of compute and data grids, automatic metadata capture from simulation studies, interoperability of data
     between simulation codes, management of data and data accessibility, management of jobs and workflow, and tools to support
     collaboration. Use of a grid infrastructure also brings certain challenges, which are discussed. These include making use of
     boundless computing resources, the necessary changes, and the need to be able to manage experimentation.

     Keywords: Grid computing; eScience; Virtual organization; Monte Carlo simulations


1. Introduction                                                             the early efforts were based on linking together high-
                                                                            performance resources, but the biggest impact is coming
Molecular simulation scientists have always needed                          from producing larger grids of more modest resources. One
significant computing resources. In the early days,                         example is the approach of linking together hundreds, or
limitations on available computing power led to a number                    even thousands, of under-used desktop machines. Consider
of constraints, such as the size of the system that could be                the example of forming a grid across a campus, and linking
studied, the length of time for which a simulation could be                 together 1000 under-used PCs. If each PC operates at
run, the complexity of the forces that could be used, and                   around 5 Gflops (a quick test shows that the author's laptop
the number of state points (e.g. temperature) that could be                 is running at 4.3 Gflops) and has 1 GB memory, a quick
used within a single study. Over the years, computer power                  multiplication shows that the grid resource has 5 Tflops of
available to computational scientists has grown at an                       power with 1 TB memory. This would equate with
exponential rate, both at the desktop and at high-                          computers around the 30th place in the world rankings
performance computing facilities, greatly increasing the                    (www.top500.org). Of course, a grid of computers does not
horizons of the simulation scientists. Growth in computing                  make a high-performance computer because connectivity
capacity has been matched by developments of new                            between separate nodes will not be fast enough to support
simulation methods and algorithms. Similarly, desktop                       parallel applications, there can be no guarantees against
visualization tools have become widely available to enable                  loss-of-service for individual nodes, and the machines on
the simulation scientist to view the results of a simulation                the grid are likely not to be of homogeneous hardware and
through graphical manipulation tools and through                            with common operating systems. Less technical, it is also
animations.                                                                 likely that different machines within a computing grid will
   The development within the past decade of grid                           be subject to different usage policies. Such a system is more
computing and e-science methods [1 ­ 4] offers the prospect                 appropriate for Monte Carlo simulations, for example,
of new evolutionary (even revolutionary) developments in                    where each node will gather a subset of the total
molecular simulations. Grid computing was developed                         configurations needed in an individual study, or for high-
with the idea of linking together computing resources to                    throughput studies where each node performs an
create large-scale computing infrastructures. Some of                       independent calculation. An example of the latter could

  *Corresponding author. E-mail: martin@esc.cam.ac.uk

                                                                  Molecular Simulation
                                    ISSN 0892-7022 print/ISSN 1029-0435 online q 2005 Taylor & Francis Group Ltd
                                                            http://www.tandf.co.uk/journals
                                                          DOI: 10.1080/08927020500065801
298                                                M. T. Dove and N. H. de Leeuw


be a simulation study over many temperatures. An example           molecular level with increased levels of realism, achieved
of the use of a grid environment to accumulate statistics and      through being able to use larger samples, more complex
temperatures is a study of diffusion of ions through               systems, or through increased accuracy to better handle
interfaces by Monte Carlo methods [5].                             changes in chemical bonding [26]. The science appli-
   Grid computing gives the prospect of what has been              cations concern issues such as nuclear waste encapsulation
described as "boundless computing" [6] in that there is a          [16,17,27,28], adsorption of organic pollutants on soil
considerable wealth of underused computing power in                particles [18,19], and surface processes, weathering and
many institutes [7,8]. The default configuration for many          precipitation of minerals [29 ­33]. The wider aim of the
PCs is equivalent to the supercomputing capabilities of            project is to develop a cross-institute collaborative
just a few years ago in terms of processing speed and              infrastructure that can be used by the scientists to
processor memory, and hence these machines are capable             accomplish the scientific objectives [20].
of being used as compute engines for molecular                        Based on the discussion in the introduction, the
simulation studies (discussed above). The challenge for            eMinerals project team has needed to take a three-track
the molecular simulation scientist is to be able to harness        approach, based on the science to be accomplished
this computer power.                                               (including the development of the simulation codes), the
   The original vision of grid computing [1] was                   grid infrastructure that has been needed to support the
characterised by the need to link together computing               science, and the virtual organization tools required to
resources, but there is a much wider vision. The challenge         facilitate the team working together. The project team
of managing simulations performed over a grid resource             consists of a mixture of scientists, code developers,
has to be met through the use of job submission,                   computer scientists and grid specialists. To some extent the
monitoring and workflow tools. With increased computing            project has been an experiment in enabling such a diverse
resources is also the need for data management methods.            team to work together towards a common objective.
Running a large study with grid resources will necessarily            The simulation work in the eMinerals project involves a
lead to the generation of many output files, too many to be        wide range of methodologies. These include both models
able to manage using conventional approaches. The data             with classical empirical potentials and quantum mech-
management challenge is further compounded by the fact             anics, the latter employing both plane wave and localized
that simulations performed on a distributed compute                basis sets. The quantum mechanical methods include both
facility will lead to data being stored in several locations.      density functional and Quantum Monte Carlo approaches.
   With the emergence of the concept of grid computing             Both methods are used for static energy and lattice
arose the concept of virtual organisations (VOs). This             dynamics methods (zero-temperature methods) and
concept arose as an independent idea, in fact without a            molecular dynamics methods (for non-zero temperatures).
necessary dependence on IT, but it is a particularly               With respect to the molecular dynamics method, one of
pertinent idea for escience where organisations come               our challenges has been to develop a molecular dynamics
together to share computing resources [9,10]. In fact,             code that can handle the necessarily large samples
collaborative working is increasingly becoming more of             required for radiation damage studies [17,27,28] in
the norm in terms of funding. In order to maximise the             systems with long-range electrostatic interactions. This
potential of simulation scientists working within a VO, it         has led to the development of the DL_POLY3 molecular
is essential for them to have access to collaborative tools,       dynamics code as part of the work of the eMinerals project
such as desktop videoconference and application-sharing            [34]. One interesting aspect of the work of the eMinerals
tools. Furthermore, the access to data needs to support            project has been to enable code developers to work with
easy data sharing, and it is essential for data to be stored in    the end users (i.e. the scientists) and to take advantage of a
a format that can be shared between different applications.        heterogeneous computing environment within which to
   This paper serves as an introduction to a collection of         test the codes.
papers [10 ­ 20] written by members of the eMinerals                  In addition to enabling scientists, code developers and
project [21], which represent an attempt to develop an             grid specialists to work together in ways that have not
integrated compute and data grid infrastructure                    happened before, the eMinerals team also recognizes the
[19,20,22 ­25] together with support to enable the project         capacity within many team members to multitask outside
team to work as a VO [9,10]. The rest of this paper gives a        their notional area of expertise. Thus, for example, some of
broad outline of the vision that drives the project.               the scientists have become members of the grid develop-
                                                                   ment team, other scientists have joined with grid specialists
                                                                   to take a leadership role in developing XML applications,
2. The eMinerals project

The eMinerals project (formal name, "Environment from              3. The vision of the eMinerals project
the Molecular Level") is one of the escience testbed
projects funded by NERC [21]. The scientific goal of the           The broad vision is to develop an infrastructure that allows
project is primarily to use grid-computing methods to              scientists to do the science they want to do, free of
facilitate simulations of environmental processes at a             the limitations of managing resources and data, free
                                                            Grid computing                                                         299


of the need to learn new tricks, free of the need to convert              analysed, and kept with the data. The approach within
data between different formats, free to collaborate, free to              the eMinerals project is to build this in to the portal
share data, and free to share resources. This vision can be               infrastructure currently being developed [37].
broken down into several components.                                 4.   Interoperability. One constant problem is that
                                                                          programs generate data in formats that prevent easy
1. Compute grid infrastructure. Shared computing                          re-use of the data in other programs. Although there
   resources, including the use of resources that may                     are many instances where data can simply be parsed
   otherwise be barely used, can be combined to produce                   from one format to another, it is also possible that the
   an infrastructure of some considerable computing                       formats of files contain exceptions (such as when
   power [1 ­4]. In fact, given the large amount on                       programs throw out a helpful line of information when
   untapped desktop resources that can be found in a                      a certain condition has been encountered). Thus
   typical institute, there is the prospect of collaborations             central to the vision is the need to be able to handle
   having access to what has been described as                            data in a general form that enables the data to be
   "boundless computing resources" [6,8]. As noted                        understood by other programs. Implicit in this is the
   below, the possibility of providing boundless resources                need for data to be self-described, which links to the
   to simulation scientists will provide new challenges.                  use of metadata. For many of our applications we are
2. Integrated data grid infrastructure. Computing and                     finding that XML provides the functionality and
   data go hand in hand, and the vision for the eMinerals                 interoperability we require. XML files can readily be
   project has at its core the integration of computing                   converted into a form that can be view via a standard
   resources and data management [19,20,22]. When jobs                    web browser, including assembling data into graphical
   run on distributed computing resources, the data                       form. The vision for the eMinerals project encom-
   generated will need to be managed in ways that hide                    passes support for the simulation scientists to obtain an
   the distribution from the user. Moreover, partners                     immediate view of the results of simulation studies,
   within any collaboration will need to be able to access                including studies in which many separate jobs are run,
   data without needing to be told specific details of the                without the tedious process of pasting numbers into
   location of files [24,25,35]. The vision for the                       separate data analysis programs [18,19,38,39].
   eMinerals project includes the need to provide an                 5.   Management of data and data accessibility. This point
   infrastructure to support collaborative and grid data                  follows from the previous points. Collaborators need to
   management, and also, as discussed in the following                    be able to share data easily. Appropriate use of metadata
   points, enable data to be understood by partners and by                and data mark-up will make the experience of handling
   the codes run by partners.                                             shared data easier, but on top of this is the need for a data
3. Automatic metadata capture. Files of data require                      archiving infrastructure that enables rapid access to the
   information about the data [36], such as when the data                 data [24,25,35]. The same metadata should be used to
   were obtained, from which simulation program, the                      enable collaborating scientists to search through the
   person who ran the simulation, and the computer that                   archives in order to obtain exactly the sets of data (which
   the simulations were run on. The file system will                      may involve many files) that are required [19].
   provide a date and file owner, but that information may           6.   Management of jobs, including workflow. Simulation
   be corrupted through moving the data file between file                 scientists tend to manage their tasks manually or through
   systems. Ideally simulation programs will provide                      bespoke scripts. A typical study will involve a number of
   headers within the data files to provide information                   discrete stages, including setting up the files, running the
   about the program (such as version number), but                        jobs, monitoring their progress and intervening if
   frequently these headers will not be propagated into all               necessary, gathering together the output data, extracting
   output files. Some of this information may be stored in                the key numbers, performing subsequent analysis and
   written documentation by the scientist, but ideally                    data presentation tasks, and archiving the data generated
   such information should be stored with the data, not in                in the study. This frequently involves the scientist in
   a physically different medium [24,25]. One type of                     carrying out a number of tedious tasks, and the
   metadata that is not built into many systems concerns                  management of complex workflow patterns may often
   the context of the data, covering issues such as the                   be the bottleneck in the scientist's productivity. Many of
   motivation for collecting the data (for example, is the                the difficulties in handling the job management and
   file a result of a production or test run, and is it part of a         workflow tasks can be solved using escience methods.
   larger series of data files, and in any case why did the          7.   Collaborative infrastructure. e-Science is beginning to
   scientist want to run this particular simulation?), and                provide the tools to enable collaborators based in
   the quality of the data (is this the best simulation that              geographically distributed locations to be able to work
   was possible at the time, or do the results look                       together as if sharing adjacent offices within a single
   suspect?). Again, some of this information may be                      building. Among the tools being developed are desktop
   captured in a notebook, but the vision is for such                     audiovisual conferencing tools and tools for sharing
   metadata to be captured automatically, whether at the                  applications. Ideally such tools should not have
   time of the submission of the job or when the data are                 significant overheads for the user, and should require
300                                                 M. T. Dove and N. H. de Leeuw


      no more effort than that is required to knock on the door     areas in which the vision can be developed, but the
      of the person in the next office along the corridor. The      challenges have yet to be explored. To mention two,
      vision is to be able to reproduce the experience of           testing the scalability for larger virtual organisations, and
      geographical proximity for distributed collaborating          inclusion of experimental data. At the time of writing, the
      scientists [9,10]. This goes hand in hand with the tools      vision of the eMinerals project is still being implemented,
      for sharing resources and data.                               and much progress is still awaited. The collection of
                                                                    papers following this introduction provides a snapshot of
                                                                    some of the technological developments that have been
4. The challenge of the vision
                                                                    made and implemented, and gives an impression of the
                                                                    science that is being carried out by the eMinerals project
The main problem with the vision outlined above is that it will
                                                                    team.
require significant changes to the way that scientists carry out
their work. In particular we identify several challenges that
face individual scientists as well as the project team.             Acknowledgements
1. Challenge of access to boundless computing. At face              We are grateful to NERC for financial support of the
   value, this challenge is counterintuitive, since boundless       eMinerals projects. We are appreciative of the support of
   computing is every simulation scientist's dream.                 the eMinerals project team.
   However, most scientists' working practices mitigate
   against making use of boundless computing. Scientists
   often prefer to handle one study at a time, and to develop
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