Non-born-oppenheimer calculations of the ground state of H ₃

We present quantum-mechanical calculations for the ground state of the H ₃ system performed without the Born - Oppenehimer approximation. In the calculations we use explicitly correlated Gaussian basis functions that explicitly depend on all of the interparticle distances. These basis functions allow us to achieve high accuracy while explicitly describing nucleus-nucleus, nucleus-electron, and electron-electron correlation effects. Gaussian basis sets ranging in size from 85 to 950 functions have been optimized using a gradient-based procedure. The issue of defining and extracting the H ₃ molecular structure based on the non-BO wave function is also discussed.