Stabilization methods for quantum mechanical resonance states of four-body systems

We describe the methods used in a computer code for quantum mechanical calculations of bound and resonance states of four-body systems. Three stabilization techniques for identifying the resonances and estimating resonance widths are discussed: calculation of coordinate-space moments, application of an imaginary optical potential, and analytic continuation of a real discrete spectrum using rational polynomial interpolation. Computational implementation of these methods, recent improvements to the computer code, and parallelization strategies are described in detail.