Mie theory helps to certain extent. But it is rather difficult to relate the particle size with absorption wavelength precisely although there exist relation. You have to use many combinations to understand exactly. This has been already dealt in research gate. Refer the below link

https://www.researchgate.net/post/Is_there_a_dependence_of_particle_size_on_light_absorption_especially_if_the_light-wavelength_is_in_the_range_of_the_particle_size

Also read the following paper it helps

J. Phys. Chem. B, 2003, 107 (38), pp 10412–10415

Actually, I'm looking for theoretical models. By that model I will be planning to create a computer program(eg-Python programming) for that.

We do this using Mie theory. I highly recommend this text:

U. Kreibig and M. Vollmer, Optical Properties of MetalClusters, Springer, 1995.

You need to assume (or calculate, or measure) the real and imaginary dielectric constants.

You can also find some empirical formulas to take into account things such as aspect ratio provided by Link and El-Sayed. They have numerous publications on the topic. Too many to list.

You should done some calculation using the mie theory if you know that your nanoparticles are spheres. If you have spheroids (such us prolates or oblates) there is also an extension of the mie theory. There some applications on the internet in webpages like nanohub.org. I hope this information help you.

@Luis,

would you please give the link of specific application in the theoretical model that in the nanohub.org

How successful you can be with Mie theory and bulk dielectric functions depends on the material and size range.

Towards small sizes, the bulk dielectric function is no longer appropriate. The limit for this is material dependent, though,.

Generally it works for smaller sizes in metals, but much less so in semiconductors, where the confinement induced changes to low energy (electron & hole ) states may dominate the optical properties.

The book by Kreiby & Vollmer is certainly a good resource to start with.