Dear all,

I started to use Mateirals Studio recently and would like to study adsorption /inhibition of small organic molecules to molecular crystals. I completed the tutorial in module ‘adsorption locator’ and tried to do some studies using the module, however, the locator seems not able to detect hydrogen bond interactions properly in my case. Here is some information about my input & output:

I tried to bind one aspirin molecule to an aspirin crystal surface. In theory, aspirin molecules bind to each other’s carboxylic group and form dimers by hydrogen bonding. Experimental studies also proved so. I followed the steps introduced in the tutorial where I built a vacuum slab over the (010) crystal facet then tried to make an additional aspirin molecule to adsorb by carboxylic groups. I used COMPASS force field and tried a lot of quality parameters (different cycles, steps, etc), but adsorption locator could not locate the aspirin additive – the additional aspirin molecule does not bind the crystal surface with hydrogen bonds, or to be precise, the additional molecule is just sitting at a random place. I was suspecting that the Monte Carlo method here failed to find a global minimum energy. I would like to know how we usually tackle this and make the adsorption locator find a true minimum energy configuration.

The following images show the simulation results. For the purposes of illustration, I removed most molecules from the crystal. Two views of the original crystal slab is shown in the second image. The third image showed the energy diagram for this trial. I would like to know what caused this failed simulation and what kind of fixes could be made.

Thanks for your inputs. Looking forward to discussing further about this software.