SCHWED-4266 Solvent Accessibility failure for deep view models

Atoms that do not actually exist are still added in deep view. The problem is
that they're added at position (9999.99, 9999.99, 9999.99). Internally we use
a grid of equally sized cubes to efficiently lookup up positions closeby.
Extreme locations lead to an extremely large grid with most of the cubes being
unoccupied. The simple solution here is to just increase the size of the
cubes. The larger the cubes, the slower the code. However, in real world
scenarios their size won't be inreased.

modules/mol/alg/src/accessibility.cc

@@ -50,6 +50,16 @@ struct CubeGrid {
     delete [] cubes;
   }
 
+  static long int NumCubes(int x_c, int y_c, int z_c) {
+    int x_cubes = std::max(1, x_c);
+    int y_cubes = std::max(1, y_c);
+    int z_cubes = std::max(1, z_c);
+    long int n = x_cubes;
+    n *= y_cubes;
+    n *= z_cubes;
+    return n;
+  }
+
   int GetCubeIdx(Real x, Real y, Real z) {
     int x_cube = std::min(static_cast<int>((x - x_min) / cube_edge_length), 
                           x_cubes - 1);
@@ -560,10 +570,23 @@ CubeGrid SetupCubeGrid(const std::vector<Real>& x,
   Real x_range = x_max - x_min;
   Real y_range = y_max - y_min;
   Real z_range = z_max - z_min;
-  Real cube_edge_length = 2 * (r_max);
+  Real cube_edge_length = 2 * r_max;
   int x_cubes = std::ceil(x_range / cube_edge_length);
   int y_cubes = std::ceil(y_range / cube_edge_length);
   int z_cubes = std::ceil(z_range / cube_edge_length);
+  
+  while(true) {
+    long int n = CubeGrid::NumCubes(x_cubes, y_cubes, z_cubes);
+    if(n <= 125000000) {
+      // n is small enough, 125000000 corresponds to a grid of size 500x500x500
+      break;
+    }
+    // we get too many cubes, let's increase edge length...
+    cube_edge_length *= 1.1;
+    x_cubes = std::ceil(x_range / cube_edge_length);
+    y_cubes = std::ceil(y_range / cube_edge_length);
+    z_cubes = std::ceil(z_range / cube_edge_length);
+  }
 
   CubeGrid cube_grid(cube_edge_length, x_cubes, y_cubes, z_cubes,
                      x_min, y_min, z_min);
@@ -678,7 +701,6 @@ void CalculateASA(const std::vector<Real>& x,
 
   int num_cubes = cube_grid.GetNumCubes();
   for(int cube_idx = 0; cube_idx < num_cubes; ++cube_idx) {
-
     if(cube_grid.IsInitialized(cube_idx)) {
       // there is at least one atom!
       SolveCube(cube_grid, cube_idx, x, y, z, full_radii,