ii ) Grow the molecule atom-by-atom. The atomistic generation algorithm continues by adding atoms one after the other, connecting each to the previous one. Because the expected geometry of the existing atom is known, we can find the allowed places to put the new atom. The forcefield rules determine the set of atom-types from which the next atom must be picked. Forcefield parameters for equilibrium bond length, angle, and dihedral are used to decide the placement of atoms in 3D space. Ideally, applying three independent constraints on 3D coordinates yields precisely one solution. Multiple possible positions are tried in the initial phase (with only 1 or 2 atoms present), as shown in Figure The energy change is calculated for each of these n positions. Finally, the i th configuration is selected from the Boltzmann distribution of these states based on the energy computed: