# Simulation of electronic potential from nanoparticles interacting with molecules

I work with SERS, where the Raman signal gets enhanced by the electric field of the nanoparticles. Now I like to simulate this kind of spectrum with Gaussian. I found a paper[1], where it looks very nice how they simulate it. They don't get a bond between the molecule and the silver nanoparticle. If I try it on my own, then the nanoparticles are thrown away by Gaussian. Has anyone of you an idea of how they simulate it? My idea is the following workflow: Frist, they optimize the attached molecule alone; after this, they made a scan with one variable. The variable is the distance between the part of the molecule where the nanoparticle should attach and the nanoparticle itself. And after this, they put the nanoparticle in the distance with the lowest energy and make a single point calculation with options to get the orbitals and the ESP mapping. It makes sense, or is it not an ordinary workflow for gaussian? I learned Gaussian myself self so I'm not sure at all.

[1] Gao, Y.; Xu, M.-L.; Xiong, J. J. Environ. Sci. Heal. Part B 2019, 54, 665-675

Additional Information: This is my route section: #p opt=vtight int=ultrafine oniom(PW6B95D3/aug-cc-pvtz:b3lyp/lanl2dz) nosymm geom=connectivity I used the OMNIC layer model and used the high layer for the molecule with PW6B95D3/aug-cc-pvtz and the low layer for the gold atom with b3lyp/lanl2dz. I have no idea how to fix the gold atom in a specific region.

• You may want to try posting the question at Materials Modeling SE, which is designed to address this kind of question. Either way, you might want to elaborate on some unclear points. For instance, "If I try it on my own, then the nanoparticles are thrown away by Gaussian." What do you mean by "throw away"? How? Why? Otherwise the workflow seems fine. Dec 10 '20 at 7:41
• I place the gold atom close to my nitro group about 2.5 Angström distance between them. When Gaussian starts the optimization, Gaussian toggles the gold atom wild around the nitro group about 10-20 Angströms and does not converge. Dec 10 '20 at 8:32
• Ok, so the position of the gold atom wrt nitro is not properly constrained? How are you applying constraints? Maybe post the Gaussian route or other info. Dec 10 '20 at 11:02
• @BuckThorn: No I do not know how honestly. My route section is: #p opt=vtight int=ultrafine oniom(PW6B95D3/aug-cc-pvtz:b3lyp/lanl2dz) nosymm geom=connectivity I directed the pyridine molecule to the high layer with the aug-cc-pvtz basisset and the gold atom to the low layer with lanl2dz basisset. Do you got a tip for me how I can perform it in a better way? Dec 10 '20 at 11:18
• No but add this info to your question and somebody here probably can. Try setting geometry constraint between the gold and nitro. Check maybe wanglab.hosted.uark.edu/g03guide/G03Guide/www.gaussian.com/g_ur/… or more recent manual Dec 10 '20 at 11:46