def extract_Heff_params(params, delta):
    """
    Processes the VUMPS params into those specific to the
    effective Hamiltonian eigensolver.
    """
    keys = ["Heff_tol", "Heff_ncv", "Heff_neigs"]
    Heff_params = {k: params[k] for k in keys}

    if params["adaptive_Heff_tol"]:
        Heff_params["Heff_tol"] = Heff_params["Heff_tol"]*delta
    return Heff_params