Curve fitting thin film reflectance to extract optical parameters

I am trying to fit experimental Reflectance data to Lorentz oscillator model but the fit is not matching the expirement data. Can you please suggest what I am doing wrong

The expression for relectivity from a thin film of thickness L is

where , and n are reflective index of incoming medium (air ), substrate(SiO2) and the thin film respectively.

where λ=532 nm is wavelength of the Laser

no=1;

and is complex reflective index.

The reflectivity is then

I am modelling the complex dielectric constant ϵ with Lorentz oscillators which gives

where , and are fitting parameter. The complex reflective index is .

I have experimental R vs E (energy in eV). I want to fit this experimental data to the above expression and find the fitting parameters.

%Resonant energy from experiment

E0=1.7226;

%Initial guess of fitting parameter

wp=0.707;

g=11.40*10^(-3);

e=10.8;

p0=[e wp g];

%Fitting of the experiment data

st=p0

opts = optimoptions(@lsqnonlin,'DiffMaxChange', 0.1,'FinDiffType', 'central', 'Display','off','MaxFunEvals',2E7,'TolFun',1E-18,'TolX',1E-300,'MaxIter',4E3);

%opts = optimoptions(@lsqnonlin);

opts.Algorithm = 'levenberg-marquardt'

x0 = st; % arbitrary initial guess

lb = 0.0*ones(size(st));

[p_estimated,resnorm,residuals,exitflag,output] = lsqnonlin(@(p)reflectance(I,E0,p) , x0, lb,[], opts)

%Function of the reflectance

function R = reflectance(I,E0,p)

ns=1.732; %reflective index of SiO2

E=linspace(min(I(:,1)), max(I(:,1)),length(I(:,1)));

E=E';

lambda=1240./E;

L=2*pi*0.6/(lambda);

I1=I(:,2);

e=p(1)+p(2).^2 ./(E0.^2-E.^2-1i.*E.*p(3));

n1=sqrt(e);

d=L*n1;

r=(n1.*(1-ns).*cos(d)+1i*(ns-n1.^2).*sin(d))./ (n1.*(1+ns).*cos(d)+1i.*(ns+n1.^2).*sin(d));

%r=(1-e)./((1+e)+2*1i.*sqrt(e).*cot(L.*sqrt(e)));

%r=(1-e)./(1+e);

R=abs(r).^2-I(:,2);

end

Below shown are plots of experiment data and data after fitting.

I have attached the experimental data. First column is energy in eV and second is reflectance.