  In the present work, we have done a comprehensive study of low-lying energy
spectrum for oxygen and fluorine chains using $ab~initio$ no core shell model.
We have used inside nonlocal outside Yukawa (INOY) potential, which is a two
body interaction but also has the effect of three body forces by short range
and nonlocal character. Also, we have performed calculations with N3LO and
N2LOopt interactions and compared corresponding results with the experimental
data and phenomenological USDB interaction. We have reached up to $N_{max}$=6
for $^{18-21}$O and $^{18-19}$F, $N_{max}$=4 for other oxygen and fluorine
isotopes, respectively. We have also discussed the binding energy of oxygen and
fluorine chains. Over binding in the ground state (g.s.) energy in neutron rich
oxygen isotopes is observed in our largest model space calculations.
