A method for determining a perturbation energy of a quantum state of a many-body system includes constructing a wave function that approximates the quantum state by adjusting parameters of the wave function to minimize an expectation value of a zeroth-order Hamiltonian. The zeroth-order Hamiltonian explicitly depends on a finite mass of each of a plurality of interacting quantum particles that form the many-body system, the quantum state has a non-zero total angular momentum, the wave function is a linear combination of explicitly correlated Gaussian basis functions, and each of the explicitly correlated Gaussian basis functions includes a preexponential angular factor. The perturbation energy is calculated from the wave function and a perturbation Hamiltonian that explicitly depends on the finite mass of each of the plurality of interacting quantum particles. The perturbation energy may be added to the minimized expectation value to obtain a total energy of the quantum state.