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Express select


Dear Scholars,
It would be really helpful if you could shed some light on express select. I am working on a nanowire having 120nm length, 20 nm radius. I want remove all the atoms on the surface. So, I have to select the atoms first to remove it. By expression select, I tried some equations for cylinder but got stuck.
Thanks in advance.
Sincerely, Ashik

Constanze Kalcher:
Dear Ashik,

the Expression select modifier requires you to enter a boolean expression. The syntax supported by the modifier is very similar to the one used by the C programming language, see Manual:

If your nanowire is aligned with the z-axis and centered at (0,0,0) try for example:

--- Code: ---Position.X * Position.X + Position.Y * Position.Y > 190^2
--- End code ---
to select all atoms with r > 19 nm.

By the way, in the latest developer version, the Construct surface mesh modifier, also has an option Select particles on the surface, which might be of interest to you.


Dear Constanze,

Thank you very much for your reply. So I am working with a nanowire that is aligned with x axis and the nanowire was carved from a whisker having 120*50*50 nm^3 and in x axis it is 120 nm. Then I carved it in 120 nm length and 20 nm radius. So the center is at (25,25) at yz plane.
I tried the code:
(Position,Z - 25)^2 + (Position,Y -25 )^2 > 190^2
But it didnt work.
Can you point out where I made mistake.

Constanze Kalcher:
Dear Ashik,

replace the commas with points, the correct syntax is Position.Z not Position,Z. Also note that the length unit here is Å not nm.



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