I am working on a goethite system, and wish to fill the unit cell with water molecules for AIMD simulation using quantum espresso. For this, some papers[1],[2] indicated the use of Grand Canonical Monte Carlo (GCMC) simulations using Towhee to find out the number of water molecules, which also pre-equilibrates the water molecules for the AIMD run.

I am totally new to MD and MC simulations. Can someone give some guidance as to how the cell can be filled with water molecules?

  1. Leung, K.; Criscenti, L. J. Lead and Selenite Adsorption at Water-goethite Interfaces from First Principles. J. Phys. Condens. Matter 2017, 29 (36), 365101.
  2. Leung, K.; Criscenti, L. J. Predicting the Acidity Constant of a Goethite Hydroxyl Group from First Principles. J. Phys. Condens. Matter 2012, 24 (12), 124105.
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    $\begingroup$ You need to input the chemical potential of water. The simulations then adds or removes water molecules to keep waters chemical potential constant. Note that there is the experimental chemical potential of water, and then, each model for water has its own chemical potential. you must decide if you want the simulation to attain an experimental or force-field determined chemical potential. $\endgroup$
    – B. Kelly
    May 16, 2022 at 9:46
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    $\begingroup$ As a further note, Cassandra can also do this, and their documentation may even have water as an example, I forget, it has been some time since I did it with Cassandra. $\endgroup$
    – B. Kelly
    May 16, 2022 at 12:04
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    $\begingroup$ Final note: there is an ideal gas contribution, as well as the residual contribution to the chemical potential. Make sure you feed the right contribution to the program. cassandra.nd.edu/images/documentation/… $\endgroup$
    – B. Kelly
    May 16, 2022 at 12:11
  • $\begingroup$ Thank you @B.Kelly for the suggestions. $\endgroup$
    – ansonthms
    May 16, 2022 at 15:27
  • $\begingroup$ @ansonthms is your problem solved now? Please update us! $\endgroup$ Dec 10, 2022 at 16:06


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