THe difference of neutral atom, atom, and ion

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AndyMao · #1 Post by **AndyMao** » Wed Jul 25, 2012 7:12 am

Dear vasp manager

I am a beginning user of vasp.
I was confused when I would like to analyze atom diffusion in condense materials. Could you tell me what the difference
is among of neutral atom, atom, and ion for the same element, and how to use them in vasp calculation.
For instance, neutral H atom, H atom, and H ion.
Does it means H atom in the POTCAR of H because its Valenz is 1? what is neutral H, NELECT= electron number +1?
what is H ion?

In addition, How to carry out vasp calculation using element isotope? Whether I change the POMASS for the mass of the isotope, for example, I change the POMSS of H from 1 to POMSS =2 for H isotope, deuterium.

With many thanks!

I`m looking forward to hearing from you!

AndyMao
<span class='smallblacktext'>[ Edited ]</span>

#2 Post by **admin** » Wed Jul 25, 2012 10:50 am

The number of electrons in a neutral atom is defined by ZVAL in POTCAR. When different number is defined using NELECT in INCAR then an ion is produced (cation or anion). POMASS = 2 in POTCAR of hydrogen atom defines the isotope deuterium.

AndyMao · #3 Post by **AndyMao** » Wed Jul 25, 2012 4:14 pm

Thanks for your reply soon!
I can understand No.2 question of isotopes.
As for No.1 question, you made me understood on the definition of ZVAL of single element. As you said, there is no different between neutral atom and atom in POTCAR for the same element, and we will obtain the ion by changing NELECT. However, for mixtures such as H2O, if I would like to insert one H cation into it, i.e., H2O+ H cation, how to calculate the NELECT? Is it the total sum of ZVAL of all elements including H and O, That is, 1x2+6-1=7? DO you think whether I need change the POTCAR expressed by the product of H and O POTCARS?

WIth many thanks!

AndyMao