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Jwk

Member

Registered: 2023-11-06

Posts: 3

Sum of electron density inside an ED isosurface

Section 4.13.8 shows how to calculate the total electron density within a defined cylinder, but how would I calculate that quantity inside, say, the 0.025 electrons/Bohr^3 surface? I wish to be able to state, for example, that "the 0.025 isosurface encompasses 85% of the total electron density of the molecule."

Last edited by Jwk (2024-11-07 23:31:59)

sobereva

Tian Lu (Multiwfn developer)

From: Beijing

Registered: 2017-09-11

Posts: 1,830

Website

Re: Sum of electron density inside an ED isosurface

A relatively easy way is:
(1) Using main function 5 to calculate grid data of electron density with grid quality as fine as possible
(2) Then enter main function 13, choose "15 If data value is within certain range, set it to a specified value", input 0,0.025, and then input 0. Now electron density lower than 0.025 a.u. has been set to zero.
(3) Finally, choose "17 Show statistic data of grid points in specific spatial and value ranges", then input "a", now the "Integral of all data" shown on screen is the number of electrons enclosed by the 0.025 a.u. isosurface.

The data obtained in the aforementioned way is calculated by uniform integration grids, note that if there are very heavy atoms, this integration will be inaccurate even if very fine grid is used because of the very sharp electron density around nuclei. In that case the best way of obtaining this quantity is using basin analysis module and use mixed-grid to perform the integration, but modification of source code is needed.

Jwk

Member

Registered: 2023-11-06

Posts: 3

Re: Sum of electron density inside an ED isosurface

Thank  you. For both water and aniline (at the B3LYP/6-31G(d,p) level of theory), the 0.025 electrons per Bohr^3 surface encompasses about 91% of the electron density.

Last edited by Jwk (2024-11-09 20:00:26)