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I need to verify that calculated vdW molecular volumes are accurate. In section 3.100.3 it states
"The principle of the Monte Carlo procedure is very simple: If we define a box (volume is L) which is able to hold the entire system, and let N particles randomly distributed in the box, if n particles are presented in the vdW region, then the vdW volume of present system is n/N*L. Of course, the result improves with the increase of N. In Multiwfn, you need to define N by input a number i, the relationship is N=100*2i, for small molecular when i=9 the accuracy is generally acceptable, for large system you may need to increase i gradually until the result variation between i and i+1 is small enough to be acceptable as converged.
I cannot find the command/location for changing N by defining i. Please advise.
Also thank you for the timely response to my previous question. I have succeeded in using Multiwfn to do the computation I required and I will of course include the citation you request in any publication. It's a very useful program!
Thank you for the prompt reply. Very helpful.
I'd like to calculate the vdW ( = iso electron density) surface integral of the square of the ESP.
surface integral (vdW) (phi )^2 dA
This integral is useful for estimating Abraham parameters as demonstrated in
Arey, JS, WH Green, and PM Gschwend. “The Electrostatic Origin of Abraham’s Solute Polarity Parameter.” JOURNAL OF PHYSICAL CHEMISTRY B 109, no. 15 (April 21, 2005): 7564–73.
I suspect that it can be calculated by squaring the ESP cube and using that as the mapped function. Is this possible and straightforward? I'd appreciate sending the workflow required.
I've just encountered Multiwfn and it is a wonderful analysis program. I look forward to using it and passing it along to my colleagues that use quantum chemistry to solve environmental engineering problems.
There are two definitions of the statistics: average, variance etc of the ESP
Manual page 145
Statistics are weighted by the facet surface areas
e.g. Vs bar = (1/ Atot) Sum (i=1 to N) Ai Fi
Manual page 140
e.g. Vs bar = (1/t) Sum (k=1 to k=t) V(rk)
Which of these statistics is computed for the command sequence
Multiwfn < H2O_fchk_v1.inp > H2O_fchk_v1.out
H2O_fchk_v1.inp
which contains
H2O_gas.fchk
12
0
The output file is
H2O_fchk_v1.out
which contains
================= Summary of surface analysis =================
Volume: 189.82511 Bohr^3 ( 28.12918 Angstrom^3)
Estimated density according to mass and volume (M/V): 1.0635 g/cm^3
Minimal value: -33.30519 kcal/mol Maximal value: 43.10833 kcal/mol
Overall surface area: 160.97471 Bohr^2 ( 45.07752 Angstrom^2)
Positive surface area: 80.20354 Bohr^2 ( 22.45928 Angstrom^2)
Negative surface area: 80.77117 Bohr^2 ( 22.61823 Angstrom^2)
Overall average value: 0.00270967 a.u. ( 1.70034 kcal/mol)
Positive average value: 0.03701499 a.u. ( 23.22728 kcal/mol)
Negative average value: -0.03135457 a.u. ( -19.67530 kcal/mol)
Overall variance (sigma^2_tot): 0.00060805 a.u.^2 ( 239.43218 (kcal/mol)^2)
Positive variance: 0.00036929 a.u.^2 ( 145.41673 (kcal/mol)^2)
Negative variance: 0.00023876 a.u.^2 ( 94.01545 (kcal/mol)^2)
Balance of charges (nu): 0.23847813
Product of sigma^2_tot and nu: 0.00014501 a.u.^2 ( 57.09934 (kcal/mol)^2)
Internal charge separation (Pi): 0.03422669 a.u. ( 21.47759 kcal/mol)
Second question
How to output the ESP for each facet and the area for each facit and the electron density of each facet.
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