DIMS is a Direct-method program of solving
Incommensurate Modulated Structures or,
it can also be regarded as a program of Direct methods In
(Fu et al., 1994, 1997;
Li et al., 1999). DIMS is based on the multidimensional
direct methods developed in our research group (Hao et al., 1987;
Fan et al., 1993; Sha et al., 1994;
Mo et al., 1996) and the Rantan phasing procedure
developed in Professor M.M. Woolfson’s group in York, England (Yao,
The program is for solving incomensurate one-dimensionally modulated structures and composite structures consists of two sub-systems. For incommensurate modulated structures, amplitudes of normalized structure factors, E-values, are calculated independent of atomic scattering factors, hence diffraction data from X-rays, electrons or neutrons can be treated in the same way. However, for composite structures DIMS can deal with only X-ray diffraction data.
DIMS possesses facilities for ab initio phasing of main reflections, hence it can also be used for phasing 3-dimensional diffraction data from conventional structures. However, this is not recommended, since we have a much more powerful tool, the program SAPI, for solving conventional and commensurate modulated structures (superstructures).
There are two versions of DIMS in VEC. One is merged with other VEC functions, while the other is stand-alone. Both can be invoked within the VEC platform. The former is used for deconvolution and phase extension for ordinary structures, while the latter is used for ab-initio determination of incommensurate modulated structures. In this section, the latter is described in details.
Fan, H.F., van Smaalen, S., Lam, E.J.W. & Beurskens, P.T. (1993). Direct methods for incommensurate intergrowth compounds I. Determination of the modulation. Acta Cryst. A49, 704-708.
Fu, Z.Q. & Fan, H.F. (1994). DIMS --- a direct method program for incommensurate modulated structures. J. Appl. Cryst., 27, 124-127.
Fu, Z.Q. & Fan, H.F. (1997). A computer program to derive (3+1)-dimensional symmetry operations from two-line symbols. J. Appl. Cryst., 30, 73-78.
Hao, Q., Liu, Y.W. & Fan, H.F. (1987). Direct methods in superspace I. Preliminary theory and test on the determination of incommensurate modulated structures. Acta Cryst., A43, 820-824.
Li, Y., Wan, Z.H. & Fan, H.F. (1999). MIMS — a program for measuring 4-dimensional Fourier maps of incommensurate modulated structures. J. Appl. Cryst.,32, 1017-1020.
Mo, Y.D., Fu, Z.Q., Fan, H.F., van Smaalen, S. Lam, E.J.W. & Beurskens, P.T. (1996). Direct methods for incommensurate intergrowth compounds III. Solving the average structure in multidimensional space. Acta Cryst. A52, 640-644.
Sha, B.D., Fan, H.F., van Smaalen, S., Lam, E.J.W. & Beurskens, P.T. (1994). Direct methods for incommensurate intergrowth compounds II. Determination of the modulation using only main reflections. Acta Cryst. A50, 511-515.
Yao, J. X. (1981). On the application of phase relationships to complex structures XVIII. RANTAN—Random MULTAN. Acta Cryst., A37, 642-644.