The buildings must be separated sufficiently to preclude pounding. If this is in the US, ASCE 7-16 requires a seismic gap of the sum of the squares of the inelastic drifts of each building. Seismic gaps are then covered with special joint covers that allow movement but seal the gap. One thing that is often overlooked is the sealing material in these seismic joints. The width of the seismic gap should be detailed such that including the hardware of the joint and the compressed sealing material, your minimum net gap is what you have calculated above.
If you google "Seismic Joints" you will find sufficient pictures to give you an idea of what needs to happen. Engineers typically don't specify a joint, just the minimum net gap required.