# Specific heat capacity at constant pressure formula

I want to calculate the specific heat capacity at constant pressure for a single walled carbon nanotube by using fluctuation in enthalpy. The fluctuations were obtained from molecular dynamics simulation. I read some literature for the method of calculation. I am faced with two formulae for the calculation of specific heat capacity, but I'm not sure which one is true: $$c_p=\frac{\langle\delta H^2\rangle}{k_B T^2}$$ was written in J. Phys. Chem. C 2010, 114, 19, 8717–8720 (Eq. (1)) . On the other hand, in the article Phys. Rev. B 74, 155441 (2006) (Eq.(4.1)) they mention a different equation from the one above: $$c_p=\frac{\langle\delta H^2\rangle}{N k_B T^2}$$

where $$N$$ is the number of atoms in the simulation. Please help me to clarify the right equation.