DIMS is a Direct-method program of solving
Incommensurate Modulated Structures or,
it can also be regarded as a program of Direct methods In
Multidimensional Space
(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,
1981).
References
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.