I have found that it is the spatial fourier transform of gs(r,t). But gs(r,t) is calculated at a particular time. So what time should I select? And then for the fourier transform which k value should I use? Since I am not familiar with fourier transformation can you suggest me which algorithm should I use?
Either you can do the Fourier transform of this quantity or you can directly calculate intermediate scattering function by the formula attached here. The averaging is the ensemble average which is generally being done from the time trajectory given that your system is ergodic. Basically, one can theoretically derive those expression from the spatial fourier transform of pair-pair correlation function, gs(r,t).
If you want to follow the direct path (calculating from gs(r,t)), then you can choose the time interval 0,5, 10, 15 or any regular timestep interval upto a large value - lets say 100000 timesteps. Please remember you have to have the trajectory snapshots which are consistent with these interval.
Thanks.
Mir Karim thank you for your answer. I have calculated the self-part i.e. Fs(k,t). But when calculating the distinct part, I am facing some problem. The plots are not looking what it should be like. I have calculated from the co-ordinates not from the fourier transformation of the Gd(r,t).
May I know which system you are working on? Is it polymer melt, colloidal solutions etc? Because for solid amorphous polymers, you may not get that properly. I am assuming your system is properly equilibrated before starting this calculation and minimum image distances were considered in that calculation.
I am working on Deep Eutectics. I have simulated 0.78 acetamide + 0.22 LiBr. The equilibrium is fine. I have calculated the incoherent intermediate scattering function at different wave vectors. The plots look as it should be. The problem comes when I am trying to calculate the coherent Intermediate Scattering Function.
Hi, I am trying to calculate the incoherent intermediate scattering function for a simple MD simulation of repulsive point particles. Can you please verify if the expression I am using is correct? : (angular brackets = ensemble avg., N=no. of particles, SUM is over particles)
For some reason the shape of the F_s(k,t) changes completely if I sample longer times. If the expression is correct, and I am not missing any prefactors, then I would know that there is some other issue. Thank you..
Thank you for your response Suman. I am now trying to see if this problem disappears on equilibrating longer before sampling, as previously my equilibration times were very short.
Hi Suman, after longer equilibration, the previous issue has disappeared. However, I wanted to ask, have you ever encountered negative values for your incoherent intermediate scattering function? Because I obtain negative values for Fs(q,t) at long times for high densities. Or do you consider the absolute value of sin(qr)/(qr) in your calculations?
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