When discussing computer software, it is impossible to ignore the on-going cost associated with maintenance and evolution of the software. This phenomenon is well understood by anyone who uses computers in their daily life. Even for our personal computers, there is a continuing level of effort associated with fixing bugs in, as well as adding new features to, the software. The need for maintenance and evolution of scientific and engineering software is several-fold greater. This is a result of the extraordinary complexity of the software coupled with the continual development of new methods resulting from increased scientific understanding and the technological upheaval associated with the often rapid evolution of cutting-edge computing technologies.
In the early formative years of NWChem development prior to the first official release of version 1.0 in 1997, it was critical to get the software out to users as quickly as possible, as often as possible, and always “for free.” This allowed feedback from the users, including bug reports and fixes, as well as established a large user base. In addition, early usage generated revised user requirements, e.g., a very important element of computational chemistry (Density Functional Theory) was added to the development effort (in 1993) after the project had already been initiated. The first beta releases of NWChem occurred in 1994 with subsequent trial releases occurring annually until the first official release in 1997. This also allowed the team to get experience on the eventual mechanisms deployed for maintenance and operations.
The initial NWChem development platform was a KSR-2 – this system was appropriate for exploration of programming models for both shared and distributed memory implementations. The first actual production hardware (an IBM SP2) and, in fact, all subsequent production hardware systems were purchased based on NWChem requirements and benchmarks. Since the initial development of NWChem, the program has been ported to a broad range of computer systems, from IBM systems running AIX, SGI IRIX and Altix systems, and HP systems running HPUX, Tru64 and Linux to Apple personal computers running OS X. In addition, the performance and capabilities of NWChem have increased substantially since version 1.0 was released in 1997. The latest version (4.7) includes many improvements to the algorithms used in NWChem as well as the ability to perform many new types of calculations.
Unlike many other supercomputing facilities, EMSL’s Molecular Science Computing Facility supports a software development effort for NWChem and related software as well as supercomputer operations. The High Performance Software Development Group is presently led by Theresa Windus. Within this group, the Molecular Science Software project is responsible for the evolution, distribution, and support of Ecce, an extensible computational chemistry environment, and ParSoft, a set of software tools for massively parallel computers, as well as NWChem. In the High Performance Software Development Group, there are five computational chemists associated with evolution, distribution and support of NWChem—the same number (but not necessarily the same people) that were originally involved in the development of the software. It should be noted that the integration of NWChem with Ecce (the user interface) was much more difficult to achieve than originally anticipated. The integration process should probably have been initiated in 1995 (two years prior to the first official release in 1997).
