The present work deals with the calculation of a screened van der Waals contribution to the binding energy of heavy alkali metals, namely K, Rb, and Cs. Our calculations show that the van der Waals contribution is of the order of energy difference between different phases for a heavy alkali metal. Further we study the effect of the Born–Mayer type repulsive interactions on the crystal structure for heavy alkalis. It appears from this study that these repulsive interactions are important in the determination of the crystal structure, particularly for a heavy alkali metal under high pressures.