## I. INTRODUCTION 

Nuclei being far from the bottom of the stability valley are studied extensively at the experimental facilities with radioactive beams. One of the fruit of these type of research is the production of the light exotic nuclei. Let us refer to e.g. a recently identified new double magic nucleus the $^{24}$O [1] at the neutron drip line. The exact location of the particle drip lines limits the region for these studies and it is intensively investigated both by experimental and theoretical methods. Theoretical prediction of the drip lines is based on mass (binding energy) calculations since particle separation energies can be easily deduced. 

There are two important theoretical frameworks for global mass calculations. Microscopic HF or HFB calculations with sophisticated effective density dependent interactions are very successful in this field. In the best HFB mass formula so far [2] the rms error is 674 keV [3]. In earlier HF calculations [4, 5] this number was somewhat larger, namely 805 keV and 822 keV [3]. In order to achieve this improved fit a new parameterization of the effective nucleon-nucleon interaction has been introduced and the pairing interaction was treated differently than in the earlier calculations. 

Surprisingly a more simple alternative procedure in the framework of the so called macro- scopic microscopic (MM) formalism can compete with the microscopic calculations in the calculation of the binding energies. The rms error in the MM calculation is 676 keV. We may say that the quality of the microscopic and MM methods are the same. Despite the almost identical global fits however the microscopic and MM methods show considerable differences when the neutron drip line is approached [3]. 

The key quantity of the MM calculations is the shell correction. The concept of the shell correction was suggested long time ago by Strutinski [6, 7] and it is still in use. E.g. in a recent global mass calculation [8] the basic ingredient of the shell correction method the smoothed single particle density is calculated in a semi-classical way by the Wigner– Kirkwood expansion. The other elements of the Strutinski method was not altered. 

Since the invention of the shell correction there were several refinements of the original method. Besides the original energy averaging, a smoothing in the particle number space was introduced [9, 10]. Even a combination of the two averaging spaces was considered [11]. The particle mean field, the simple harmonic oscillator or Nilsson potential was replaced in the calculations by more realistic phenomenological forms in which the spectrum has a 

