Crystallography in Canada 

A. C. Larson in Canada

Allen C. Larson  

Reprinted from CNCC Newsletter No 1 (Canadian National Committee for Crystallography) September 2009

Fig 1: Dr. Larry Calvert (left)
and Dr. Eric Gabe (right)

Fig 2: Allen C. Larson in a style of
clothing more typical of Canada
(circa 1981)


I had joined the Los Alamos Scientific Laboratory (LASL) in 1956 after graduating from Washington University with a PhD. Working with Don Cromer and Brad Roof studying the structure of alloys of plutonium. One of my principle activities was developing software for determining and refining the crystal structures of these phases. I quickly established myself as an excellent software developer using the LASL developed Madcap language on the MANIAC (a LASL developed computer) and very soon after that Fortran on the IBM computers at LASL. In 1966, I was elected to the Computing Committee of the American Crystallographic Association and made a member of the IUCr Computing Committee and chaired the Committee from 1975 to 1978. Then I was a consultant to the committee again until 1981, a total of twelve years with the IUCr Computing Committee. 


We noted that many of the alloy structures we were finding were similar to already known structures. In an effort to enable us to solve the structure of the new phases which our metallurgists were creating, we decided that developing a computer based data set of the known structures was necessary. In the summer of 1960 we had a summer Graduate Assistant, Joe Finny, search the literature and enter the details of known metal and alloy structures into our data file. 


In the summer of 1973 Los Alamos Scientific Laboratory was having a funding crisis and needed to reduce its staff. They assembled a list of people to place on the RIF (Reduction In Force) list. Unfortunately for me, I was placed on that list. I did not want to abandon crystallography as they insisted I would have to if I were to take an alternate position within the laboratory, so I opted to accept the RIF pay and leave the laboratory and moved with my family to Austin, Texas where my wife had enrolled in the Law School at the University of Texas. 


I contacted several people around the US and in Canada in the weeks following receipt of the RIF notice. One important person on that list was Dr. W. B. (Bill) Pearson who was at NRC in Ottawa. One of my concerns was the metals data file that Dr. Don Cromer and I had started to construct at Los Alamos. We felt that that project would be lost after I left Los Alamos. I asked Dr. Pearson if there was anything I could do to find a new home for it. He invited me to bring it to NRC where Dr. Larry Calvert, who was doing a lot of work on the IUCr Structure Reports metals data, accepted responsibility for it. 


I flew to Ottawa with the metals data file and with the software that we had developed to access the file on a magnetic tape. Dr. Calvert and Dr. Gabe had a DEC PDP-8 which we used to further develop the data file and its software. This machine had been greatly enhanced from to 4096 12 bit word PDP-8 that I had been using in Los Alamos for diffractometer control. 


After completing the transfer of the file, Calvert and Gabe asked me to install Multan on the PDP-8. I had worked on doing that on a small computer for Syntex in Cupertino late in 1974 and agreed to do this new task. And after we finished that it was agreed that I should install other portions of the Los Alamos Crystal Structure package on the PDP-8. This included the Space Group symbol interpreting software that I had developed on sabbatical year in Cambridge and Los Alamos. However since I had installed that package on the Syntex hardware, we decided that perhaps it would be best if I wrote a new program. Thoughts about licensing drove us to this decision. The accuracy of the new program was checked by comparing its output with that of the original program that had been very carefully checked manually against the International Tables For X-Ray Crystallography, 1952. The new code uses matrices and vectors to develop the groups where the older code had developed its operations by scanning a list of binary numbers that I had developed. The new code was carefully documented internally, the older code was not nearly as well documented internally. This new code is the one that is used in the GSAS package today. 


In the summer of 1978 Eric Gabe and I presented the NRCC software package at the IUCr Computing School in Enschede, The Netherlands. I was partially funded by the IUCr on this trip which included the IUCr Meeting in Warsaw, Poland. 


My last major stay in Ottawa was from 15 November 1980 to 15 February 1981. On this trip Eric Gabe and I started to develop a powder data refinement capability into the software package. I was back in June 1981 for the IUCr meeting that year, now funded by Los Alamos National Laboratory that had rehired me on 1 June 1981. 


In the seven years that I was self-employed I also spent two months at The University of Calgary working with Dr. K. Ann Kerr, again installing and developing crystallographic software. This was in two separate one month long stays, the first June 1975, the second in March 1976. 


My duties on returning the Los Alamos were to support the diffraction instruments at LANCE, the Los Alamos Neutron Scattering Center. I initially was to support a single crystal instrument. But since they wanted to develop a powder instrument as well was asked to help developing software to analyze its data as well. Prof. Robert Von Dreele at ASU was one of the people involved with developing the powder diffraction capability and he assisted me in expanding the capability Los Alamos crystal structure software to be able to refine structures against powder data. 


One of the criteria that I always use in developing software is to keep it open to addition of new data sources and new output products. With this in mind Bob and I continued the process of inserting powder data refinement into the Los Alamos Crystal Structure package. I had been thinking of a name for our software system and came up with 'Generalized Structure Analysis System'. After a bit of thought we decided that we should drop the 'ized' in that name and thus the 'General Structure Analysis System', GSAS, came into being.