The LSPR of nanoparticles does not peak at the bulk plasma frequency, because of electromagnetic confinement effects. To predict the LSPR frequency, one has to calculate the nanoparticle polarizability or extinction cross section. This requires as input the dielectric function of the material constituting the nanoparticle. For "common" plasmonic materials such as silver or gold, using the bulk dielectric function works quite well to get the LSPR frequency, except for very small, few-nm nanoparticles. For "unconventional" plasmonic materials such as gallium or other p-block elements the situation is less clear, as there are not so many studies on the topic. However, starting with the bulk dielectric function is always a wise choice. For gallium, it is also worth knowing if the material is in the solid or liquid state because of its near room temperature melting point. See for instance ACS Nano 9 (2), 2049–2060 (2015) or Opt. Mater. Express 6(7) 2434-2447 (2016)

Hi Prithu, my understanding of the effect is that the bulk frequency applies but is shifted due to the confinement in the particle. This is usually modeled by taking the bulk plasma frequency and solving maxwells equations with the boundary conditions of your particle to determine the actual resonance. More details on this, and some code for modeling the effect can be found in this book: https://www.springer.com/gp/book/9783540578369

In addition to the above reply, I can say that bulk plasmon frequency is the important parameter. The observed resonance frequency in the case of nanoparticles depends on the bulk plasmon frequency, the shape and size of the nanoparticles as well as on the refractive index of the surrounding media. Details about this can be found in papers given below.

1. Applied Optics 51 2606 (2012)

2. Ind. J. Phys. 90 107 (2016)

The LSPR of nanoparticles does not peak at the bulk plasma frequency, because of electromagnetic confinement effects. To predict the LSPR frequency, one has to calculate the nanoparticle polarizability or extinction cross section. This requires as input the dielectric function of the material constituting the nanoparticle. For "common" plasmonic materials such as silver or gold, using the bulk dielectric function works quite well to get the LSPR frequency, except for very small, few-nm nanoparticles. For "unconventional" plasmonic materials such as gallium or other p-block elements the situation is less clear, as there are not so many studies on the topic. However, starting with the bulk dielectric function is always a wise choice. For gallium, it is also worth knowing if the material is in the solid or liquid state because of its near room temperature melting point. See for instance ACS Nano 9 (2), 2049–2060 (2015) or Opt. Mater. Express 6(7) 2434-2447 (2016)

Bulk and surface plasmons in highly nanoporous gold films

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.858.4227&rep=rep1&type=pdf