Om Aim Hrim Klim
Chamundaye Viche Namaha
This mantra is referred in Yoga Vidya tradition as shakti mantra. It harmonizes and energizes all the chakras (energy centers in the astral body).
Aim is the bija mantra of Saraswati. Hrim is the Bija Mantra of Durga, Klim is the bija mantra of Lakshmi. Chamunda is a name of Kali.