Hello all. I am a synthetic inorganic chemist who worked on gold clusters for application in heterogeneous catalysis during my PhD few years ago. Now I am trying to learn some computational calculations (I am a beginner) to gain insight and (as complementary knowledge) about catalytic reactions using metal clusters. Here is the case: I made Ru3(CO)12 and deposited on TiO2 nanoparticles (30 nm) for photoreduction of CO2. There is some evidence from XAFS data that there is a significant population of Ru3 on TiO2 (and of course aggregated, larger ones). I have been reading about DFT, Ab Initio, semi-empirical methods but some are hard to grasp by a synthetic chemist like me. What I want to do is to calculate the interaction of CO2 with Ru3 clusters on TiO2 like the binding energy of CO2 on Ru3 clusters, adsorption/desorption and dissociation of CO2 on Ru3 clusters. My questions are:
1) what kind of quantum mechanical calculations is more accurate or preferred (faster with some approximations)? Is it DFT or Ab initio or Molecular Mechanics/Dynamics or Quantum Monte Carlo or semi-empirical or some other methods?
2) is there free software/program to perform such calculations. I know Quantum Espresso, Orca, GAMESS, VASP are free-of-charge. What about free DFT software/program packages? Are there any?
3) is it possible to do with a normal laptop at home (without super large memory and disk from computational facilities at institution/university/research centre?
I talked to some computational chemists and they told me even for such a small system, it takes ages to perform such calculations - they also advice me that I could do another PhD for computational calculations because it takes years to learn. :-) First, DFT scales with N^3 (or N^4?) as the number of atoms increase. Plus, interaction of CO2 with Ru3 clusters is not quite ideal because my catalyst is Ru3/TiO2. CO2 might adsorb on Ru3, or at the interface between Ru3 and TiO2, or at TiO2 but dissociate at Ru3 clusters. And finally they told me that normal laptops don't work no matter how expensive the laptop is i.e. great memory and disk. Eventually I need a desktop connected to computational facilities at a university/institution/research center.
Any advice where should I start?
I am a VASP user (VASP is not free), when I started to perform calculations with VASP I used my laptop to optimize Fe3O4 clusters up to 113 atoms. But the calculations were very slow, it takes a lot of time in a regular laptop. Now I am using a supercomputer with 192 processors and I can calculate Fe3O4 clusters up to 1211 atoms!!!! So, I would suggest to get time from a supercomputer center, VASP is a very nice package, but if you don't have access to this software you could try with Quantum Espresso, which is free.
Regards
>>>1) what kind of quantum mechanical calculations is more accurate or preferred (faster with some approximations)? Is it DFT or Ab initio or some other methods?
You are going to model periodic systems...You should be using DFT methods. Ab initio is time consuming
>>>2) is there free software/program to perform such calculations. I know VASP and Quantum Espresso are free-of-charge.
VASP is not free, Quantum Espresso is free
>>>3) is it possible to do with a normal laptop at home (without super large memory and disk from computational facilities at institution/university/research centre?
No you will not be able to perform these calculations on a laptop at home ...if you do then you cannot use your laptop efficiently for anything else, since the calculations will take up both disk space and memory
You will need a supercomputer with multiple processors so you can run it as an mpi job
As you mentioned, you are a synthetic chemist and if you do not have any computational chemistry background, I suggest you collaborate with a computational chemist who has an expertise in periodic systems to simulate your systems.
Also, please try to do some thorough literature search, where someone might have already done such simulations to give you a much better idea where and how to start
I hope this helps
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