how to output the atom/swap probability

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1

Dear Lammps user,

I want to get the information of acceptance rate when using the fix atom/swap command. I tried to output it in thermo with fix ID, but there will be error : Thermo fix does not compute scalar (…/thermo.cpp:889)

Also if I try to use fix ave/time, it gives a similar error: Fix ave/time fix does not calculate a scalar(…/fix_ave_time.cpp:220).

How should I output that fix value?

Thank you!

Regards,
Shenli

2

Dear Lammps user,

I want to get the information of acceptance rate when using the fix
atom/swap command. I tried to output it in thermo with fix ID, but there
will be error : Thermo fix does not compute scalar (../thermo.cpp:889)

Also if I try to use fix ave/time, it gives a similar error: Fix ave/time
fix does not calculate a scalar(../fix_ave_time.cpp:220).

How should I output that fix value?

how about simply reading the documentation?
from the documentation of fix atom/swap:

This fix computes a global vector of length 2, which can be accessed
by various output commands. The vector values are the following global
cumulative quantities:

1 = swap attempts
2 = swap successes
The vector values calculated by this fix are “extensive”.

divide the second number by the first and you have your acceptance rate.

axel.

3

Dear Axel,

Thank you for your reply. I got the value of total swap attempts f_ID[1] and successes times f_ID[2], but the total attempts number is always zero. My original fix command:
fix 5 cation atom/swap 200 10000 5829017 1500 types 2 3

and I output the fix every 200 steps
Wouldn’t the swap attempts be equal to 10000 for each output?

4

Dear Axel,

Thank you for your reply. I got the value of total swap attempts f_ID[1] and
successes times f_ID[2], but the total attempts number is always zero. My
original fix command:
fix 5 cation atom/swap 200 10000 5829017 1500 types 2 3
and I output the fix every 200 steps
Wouldn't the swap attempts be equal to 10000 for each output?

no, just read the docs!!

the fix outputs the *total* number of attemps, so you'd get 0, 10000,
20000, 30000, and so on for your fix.

i just tried with the latest development version and it works just fine for me.
defining a variable for the success ration is a bit tricky, because of
the initial step having no attempts yet, but the following workaround
does the trick:

variable success equal f_ID[2]/((f_ID[1]<1)+f_ID[1])

axel.

5

Thank you Axel. It works fine now.

6

Thank you Axel. It works fine now.

it always worked. :wink: