GROMACS version: 2020.2

GROMACS modification: No

Is it possible to compute isothermal area compressibility in GROMACS directly?

I try to do it by computing that in excel, but I am not sure that everything is ok, so please check

To do that I get value box-x and box-y from gmx energy. and compute area per lipid X*Y/100 (my number of lipid in leaflet), so I have 0,70 nm^2 and standard error 0,01 nm^2

From there https://pubs.acs.org/doi/pdf/10.1021/acs.jpcb.6b01870

I take the mathematical formula to calculate isothermal area compressibility modulus

kB is the Boltzmann constant, T - the simulation temperature, ⟨AL⟩ the average area per lipid, and sAL the standard error of AL, nL number of lipids.

In my case

kB = 1.38064852 × 10-23 m2 kg s-2 K-1, but I have in nanometers my area per lipid so I change to

1.38064852 × 10-5 nm2 kg s-2 K-1 = 1.38064852 x 10-5 nm2 g s-2

T = 300K

= 0,69 nm^2 (69 A^2)

nL = 100 lipids (I have 100 lipid in one leaflet, my bilayer system consists of 200 lipids)

sAL = 0,01 nm^2

so:

2*1.38064852 × 10-5 nm^2 kg s^-2 K^-1 * 300 K * 0,7 nm^2

------------------------------------------------------------------------------- =

100 * (0,01 nm^2)^2

2*1.38064852 × 10-5 nm^2 kg s^-2 K^-1 * 300 K * 0,7 nm^2

------------------------------------------------------------------------------- =

100 * 0,0001 nm^4

After reduction

0,005796 kg s^-2

------------------------------------------------------------------------------- =

0,01

0,5796kg

------------- = but I must change to mNm^-1 like in article, so

s ^2

0,5796 kg * m

---------------------- =

s ^2 * m

0,5796 kg * m

---------------------- =

s ^2 * m

If:

N = kg * m * s^-2

so:

0,5796 N * m^ -1, but I must have mNm^-1, so 579,6 mN*m^-1

Do you think that is ok? Exp IACM is 180-330 for 298 K