Questions regarding H2 adsorption onto nanolayer
Posted: Wed Nov 02, 2022 1:34 am
Hi all,
I'm quite new to the world of computational chem. I'm working on an independent project as part of my final undergrad unit. I'm studying the adsorption of H2 onto a BeN nanosurface, but have run into some issues with interpreting some of my initial findings, or even whether I'm running the right computations. Unfortunately, my supervisor is on extended leave and it not able to answer my emails at the moment, so I'm finding answers hard to come by.
I'm using VASP and ran a DFT relaxation just fine on the underlying structure. Then I ran some further DFT relaxation tests with H2 at different positions above the sheet. They all worked fine and I was able to determine the apparently most favourable position. However, I am running into issues now with actually trying to investigate the adsorption of multiple H2 molecules. I tried to follow this tutorial on the VASP website for H2O onto TiO2. It seemed that once I had the relaxed surface geometry and a place to put the H2 molecule(s), then you run an MD computation. I modified my INCAR file to match their additions:
IBRION = 0
POTIM = 1.
MDALGO = 1
PROB = 0.9
TEBEG = 10; TEEND = 10
However, in their INCAR, ISMEAR is meantioned twice. As ISMEAR=2 and ISMEAR=0. Is this needed? I would imagine that VASP would ignore one or the other. Then I wrote an ICONST file to maintain the bond length of the H2 molecules.
However, the results were...odd.
With only 1 H2 molecule the H2 starts at ~2.5A and then retreats to ~4.5A.
PRE: POST: When I have 2 H2 molecules at ~2.2A in different (what I believed to be favourable from earlier DFT calculations) spots, one molecule retreats to ~3A and the other goes through the layer to the other side at ~2.6A. Additionally, the geometry of the BeN2 layer changes for both computations.
How am I supposed to interpret this? Does this mean that the surface is not good for adsorption of H2, or am I doing the wrong type of test? I checked the OUTCAR and it doesn't look like the computations hit the minimum. Alternatively, are there any other good tutorials on how to run adsorption tests for multiple molecules?
I'm quite new to the world of computational chem. I'm working on an independent project as part of my final undergrad unit. I'm studying the adsorption of H2 onto a BeN nanosurface, but have run into some issues with interpreting some of my initial findings, or even whether I'm running the right computations. Unfortunately, my supervisor is on extended leave and it not able to answer my emails at the moment, so I'm finding answers hard to come by.
I'm using VASP and ran a DFT relaxation just fine on the underlying structure. Then I ran some further DFT relaxation tests with H2 at different positions above the sheet. They all worked fine and I was able to determine the apparently most favourable position. However, I am running into issues now with actually trying to investigate the adsorption of multiple H2 molecules. I tried to follow this tutorial on the VASP website for H2O onto TiO2. It seemed that once I had the relaxed surface geometry and a place to put the H2 molecule(s), then you run an MD computation. I modified my INCAR file to match their additions:
IBRION = 0
POTIM = 1.
MDALGO = 1
PROB = 0.9
TEBEG = 10; TEEND = 10
However, in their INCAR, ISMEAR is meantioned twice. As ISMEAR=2 and ISMEAR=0. Is this needed? I would imagine that VASP would ignore one or the other. Then I wrote an ICONST file to maintain the bond length of the H2 molecules.
However, the results were...odd.
With only 1 H2 molecule the H2 starts at ~2.5A and then retreats to ~4.5A.
PRE: POST: When I have 2 H2 molecules at ~2.2A in different (what I believed to be favourable from earlier DFT calculations) spots, one molecule retreats to ~3A and the other goes through the layer to the other side at ~2.6A. Additionally, the geometry of the BeN2 layer changes for both computations.
How am I supposed to interpret this? Does this mean that the surface is not good for adsorption of H2, or am I doing the wrong type of test? I checked the OUTCAR and it doesn't look like the computations hit the minimum. Alternatively, are there any other good tutorials on how to run adsorption tests for multiple molecules?