You have given the numerator and denominator polynomials in wrong order to the tf function, the tf function takes the numerator input polynomial coefficients first and then denominator, for more help check
R = 98.7814e-3;
L = 65.265e-9;
C = 436.876e-12;
% V is voltage transfer function, output across capacitor
V = tf([1],[L*C,R*C,1]); % tf numerator and denominator order changed
bode(Z,{40,5e8});
grid on
The value of your resonant frequency will depend on your L, and C values, In my opinion the values entered by you are not practical as resistances in the order of milli ohms are not present in standard resistance charts, this applies to your capacitor and inductor values too, you must look at the chart values.
The resonant frequency of series RLC circuit is 1/sqrt(L*C), after substituting the values entered by you for L and C we can see that the Voltage graph peaks at the same frequency(1/sqrt(L*C)) shown in the graph .
The following equation will graph the Impedance of the circuit according to me, so in order to calculate the resonant frequency, you have to mark the point where the phase is 0 deg. since at this point the impedance will be purely resistive and this will be your resonant frequency. Again this is also equal to 1/sqrt(L*C)
Z = tf([L*C,R*C,1],[C,0]);
bode(Z,{40,5e8});
grid on
I hope this answers your query
Thank you.
