# Re: FEP calculations: optimizing the dlambda, number of steps

From: Shyno Mathew (sm3334_at_columbia.edu)
Date: Mon Nov 18 2013 - 11:44:59 CST

Hello all,
I think I figured out the answers
The column before temperature is the average change in potential energy
(deltaUavg) and the column preceding it is the change in potential energy
(delta U). So I should calculate the variance of delta U values to optimize
delta lambda, length of each window?
Could some one confirm this?

thanks,
Shyno

On Fri, Nov 15, 2013 at 4:02 PM, Shyno Mathew <sm3334_at_columbia.edu> wrote:

> Dear all,
> I am doing the FEP calculations and need some help in understanding the
> .fepout file.
> 1. this is the first part of .fepout file
> # STEP Elec vdW dE dE_avg Temp dG
>
> # l l+dl l l+dl E(l+dl)-E(l)
>
>
> #NEW FEP WINDOW: LAMBDA SET TO 0 LAMBDA2 0.05
> FepEnergy: 0 -469793 -469790 34401.03 34399.75 0.8153 0.8153 298.6998
> 0.8153 FepEnergy: 100 -472878 -472876 33902.44 33900.11 0.4059 0.3622
> 313.4741 0.1558 FepEnergy: 200 -472922 -472919 33338.32 33336.3 0.8862
> 0.1122 312.7195 -0.3716
> I understand the penultimate column is temperature and the last column is
> dG value. What exactly are the other columns?
>
> 2. I am trying to see what dlambda, number of steps will give me accurate
> results.
> Following article says keeping the variance at each stage on the order of
> 1-2 KT usually guarantees good overlap between probability distributions in
> two consecutive strata and a reliable error estimate.
> Here the variance means the variance of dG values (only of the ensemble
> average, not including minimization??) for a given lambda window?
> http://pubs.acs.org/doi/abs/10.1021/jp102971x
> (talking about page 10242 of article)
> For 300 K, 1-2 KT is 0.596 - 1.192 Kcal/mol.
> The variance (considering ensemble (not minimization values) dG values
> for first window, lambd= 0 to lambda=0.05) is 0.0158. So it's one order
> lower. This means I need to change dlambda and/or change the number of
> steps after minimization?
>
> thanks,
> Shyno
>
> --
> Shyno Mathew
> PhD student
> Department of Chemical Engineering
> Columbia University
>
>

```--
Shyno Mathew
PhD student
Department of Chemical Engineering
Columbia University
```

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