A technique based on the relativistic pseudopotential method is proposed to calculate the derivative of the electronic vibrational level energy with respect to the fine-structure constant α for heavy-element compounds. The effect of a small change in α on the frequency of a transition between the vibrational levels of the ground and first excited states of the molecular cation HfF+ is calculated. This information is necessary to prepare experiments aimed at determining the time variation in the fine-structure constant. © 2008 Pleiades Publishing, Ltd.