is used, the "stiffness" of the wall can be modeled by the parameter N , where the system rapidly converges to the hard-wall limit for N → ∞. Besides providing a more realistic picture, finite confining potentials provide a grand technical advantage: They do not change the Dirichlet boundary condition and thus can be used with unmodified Gaussian basis sets, allowing an easy implementation in modern quantum chemistry packages. The pressure P acting on a closed quantum system, i.e., one with impenetrable walls, can be calculated from the virial theorem for the confined system as P (r