【LAMMPS翻译系列】min_modify命令

min_modify命令用来设置由min_style命令所选择的能量最小化算法的参数。

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使用语法

min_modify keyword values ...

• 可以使用1对或多对关键字
• keyword = dmax or line
  
  • dmax value = max
  • line value = backtrack or quadratic or forcezero

使用举例

min_modify dmax 0.2

使用介绍

该命令用来设置由min_style命令所选择的能量最小化算法的参数。不同的设置参数会影响收敛速率和能量最小化过程中需要计算力的次数。用户可以通过测试对这些参数进行调节。

cg算法和sd算法

The cg and sd minimization styles have an outer iteration and an inner iteration which is steps along a one-dimensional line search in a particular search direction. The dmax parameter is how far any atom can move in a single line search in any dimension (x, y, or z). For the quickmin and fire minimization styles, the dmax setting is how far any atom can move in a single iteration (timestep). Thus a value of 0.1 in real units means no atom will move further than 0.1 Angstroms in a single outer iteration. This prevents highly overlapped atoms from being moved long distances (e.g. through another atom) due to large forces.

The choice of line search algorithm for the cg and sd minimization styles can be selected via the line keyword. The default backtracking search is robust and should always find a local energy minimum. However, it will "converge" when it can no longer reduce the energy of the system. Individual atom forces may still be larger than desired at this point, because the energy change is measured as the difference of two large values (energy before and energy after) and that difference may be smaller than machine epsilon even if atoms could move in the gradient direction to reduce forces further.

By contrast, the quadratic line search algorithm tries to reduce the forces to zero, while guaranteeing that the energy changes is not positive (uphill). For some systems, it may also be more efficient than the backtracking algorithm by requiring fewer energy/force evaluations. The forcezero line search algorithm is similar to quadratic. It may be more efficient than quadratic on some systems.

使用限制

无

相关命令

min_style, minimize

默认设置

The option defaults are dmax = 0.1 and line = backtrack.