The Calculation Of Bio-Molecules' Electron Density

Bio-molecules play important role in life process. Studies on them have an important meaning to understand its function in biochemical reactions. The electron-density distribution of the molecules is a key physical parameter to describe the molecules' property. Many physical or chemical properties can be analyzed and calculated from molecule's electron density. Then we can analyze the force in molecules or between molecules or other properties of the molecule. But this method have some difficult to calculate bio-molecules, because time cost of traditional quantum chemistry calculations is proportional to the 4th power of the system's size. We can't finish bio-molecule's calculation, such as protein, based on current condition.But the nearsightness principle said the electron density in molecule has a finite influence to other regions. If we neglect the influence outside this range, we can get correct energy and wave functions limited by some conditions. Based on this principle, this thesis discussed the influence of transformation of the system to the electron density of other region. We also calculated the hydrocarbon chains as examples. The results show that the influence of transformation was about 4A. By using this method we calculated the protein, and got continuous electron density contour and its derivatives, which the buffer radius was specified as 8A considering there are many polar groups in the protein. While when the buffer radius was specified as 6 A, we can't get a continuous distribution of electron density. We also proposed the ways to develop this calculation method.