McLachlan A D
Medical Research Council Laboratory of Molecular Biology, Cambridge, England.
Acta Crystallogr D Biol Crystallogr. 1993 Jan 1;49(Pt 1):75-85. doi: 10.1107/S0907444992008102.
The entropy-dynamics method seeks maxima for the entropy of the electron density for N atoms in a crystal cell, when the Fourier amplitudes are fixed, but their phases are unknown. By analogy with molecular dynamics, the effective potential energy is the negative entropy V = -NS. The kinetic energy is proportional to the squared velocities of the electron densities at grid points in the map. It reduces to a sum of Fourier-mode rotor energies. Each rotor angle experiences a couple equal to the phase gradient of S, and local dynamical equilibrium yields a Boltzmann distribution of S. Discrete phase angles (e.g. signs) are treated as quantized rotor modes. The distributions depend on a popularity function of the entropy histogram. Trial calculations have been made of phase averages and correlations in a centrosymmetric projection of the membrane protein bacteriorhodopsin. The maximum-entropy solution and the correct solution do not always coincide.
熵动力学方法旨在寻找晶胞中N个原子的电子密度熵的最大值，此时傅里叶振幅固定，但相位未知。类似于分子动力学，有效势能为负熵V = -NS。动能与电子密度在图中网格点处速度的平方成正比。它简化为傅里叶模式转子能量的总和。每个转子角度所受的力偶等于S的相位梯度，局部动态平衡产生S的玻尔兹曼分布。离散相位角（如符号）被视为量子化的转子模式。这些分布取决于熵直方图的流行度函数。已经对膜蛋白细菌视紫红质中心对称投影中的相位平均值和相关性进行了试算。最大熵解和正确解并不总是一致的。
