The effects of additional cells on the circuit operation of quantum ce
llular automata (QCA) logic, proposed by Lent et al., are numerically
studied using the extended Hubbard model self-consistently. We investi
gate the differences in logic circuit operation between Lent's inverte
r and our original 4-cell one characterized by a loop structure in the
cases of 4 and 5 quantum dot cells (QDC). We find that the 4-cell inv
erter with loop structure composed of 4-QDC exhibits favorable charact
eristics in QCA logic operation.