Lanthanide (and Actinides) are difficult to handle, computationally. They tend to require relativistic methods. They also tend not to be single-determinant. (So

Lanthanide (and Actinides) are difficult to handle, computationally. They tend to require relativistic methods. They also tend not to be single-determinant. (Source: I've tried and very much failed). I'm not as familiar with QMC, so I don't know the status of QMC with relativistic methods, etc.