Method for modelling the electron density of a crystal

In a digital computer, a method for modelling the electron density distribution of a macromolecule in a defined asymmetric unit of a crystal lattice having locations of uniformly diffracting electron density, comprising:

• inputting experimental data collected from an X-ray diffraction experiment into the computer;
• randomly distributing a plurality of scattering bodies in an asymmetric unit having substantially the same dimensions as the defined symmetric unit;
• and
• repeatedly moving said plurality of scattering bodies to more compact distributions such that the total distance between scattering bodies is decreasing, and determining scattering amplitudes of the scattering bodies in each distribution until reaching a final distribution of scattering bodies, the final distribution having scattering amplitudes having a maximum fit with amplitudes from said experimental data, said final distribution also defining the electron density distribution of the macromolecule in the defined asymmetric unit.

A method for modelling the electron density distribution of a macromolecule in an asymmetric unit of a crystal lattice by X-ray crystallography comprising:

• (a) irradiating the crystal lattice with X-rays and recording experimental X-rays and recording experimental X-ray diffraction data;
• (b) determining the dimensions of a asymmetric unit of said crystal from said diffraction data;
• (c) producing an initial distribution of a plurality of spherical scattering bodies by placing each of said scattering bodies within an asymmetric unit having the same dimensions as the asymmetric unit of the crystal lattice, each of said spherical scattering bodies have a predetermined radius;
• (d) calculating scattering amplitudes of said initial distribution of scattering bodies;
• (e) determining the fit between the calculated amplitudes of said distribution and said experimental data;
• (f) translating at least one of said scattering bodies within the asymmetric unit to modify said distribution;
• (g) calculating scattering amplitudes and phases of said modified distribution of scattering bodies;
• (h) determining the fit between said calculated amplitudes of said modified distribution and said normalized experimental data;
• and
• (i) producing a final distribution of scattering bodies repeating steps (f) through (h) until the fit between said distribution of scattering bodies and said experimental data is effectively maximized, said final distribution of scattering bodies being an electron density model of said crystal.