Is the imaginary part of the relative permittivity of Au positive or negative?

Hello everyone.

Here is another question about "models. woptics. scattering_nanosphere". In this model, the imaginary part of the relative permittivity of Au is negative, e.g. the complex dielectric constant is
-16.8177-1.0668*i,
when the frequency of incident beam is 424THz. The data was extracted from
P. B. Johnson and R. W. Christy, "Optical Constants of the Noble Metals," Phys. Rev. B, vol. 6, pp. 4370-4379, 1972.
I downloaded the paper and found that the complex dielectric constant was defined as
(n+k*i)^2.
When the frequency of incident beam is 1.76eV (corresponding to 424THz), n=0.13 and k=4.103. Then the complex dielectric constant should be
-16.8177+1.0668*i.
I also checked some other papers about the data. It seems that most metals have a positive imaginary part of the relative permittivity.

Please help me to check it.
Thank you very much.