Dear all,
I want to learn about the mulliken charge distribution within the molecule. I am calculating mulliken charges using DFT method using Gaussian 09. In this regard, I need to know about what are electronegative atoms, electropositive atoms? How to find the charge transfer taking place within the molecule? When electropositivity of some atoms increases due to presence of highly electronegative atoms in its neighbouring positions how to interpret them? Kindly help me in knowing the basics and to go ahead with the mulliken analysis.
Thank you all in advance......
please see the following pdf, it may answer you:
http://www.cem.msu.edu/~cem883/topics_pdf/population_analysis.pdf
do you want calculate fukui index ? i guess that gaussian make population analysis
The mulliken charges are charges based in the local electron density (charge density) its depend strongly of the basic set and the functional, because it is sensitive to the probability density . soo if you what to compare results you should use the same functional and basic set in the way to make a accurately comparison. In other way the comparison is not adequate due to the change of probability density in each method .
i hope that this be useful for you.
Dear all,
Thank you for your kind interest and suggestions made. Dear Carlo, I am intersted in fukui index also. Kindly give me some suggestions in understanding its basics and how to calculate them.
Regards,
V.Ragavendran
If you are interested in calculating Fukui index, first you will need to choose which approach you want to use for there are many. Usually Mulliken charges are consistent using different methods, but it strongly depends on the basis set. You could use natural population analysis instead or use the fragment molecular orbital approach that uses the coefficients of the molecular orbitals instead of using charges, but in this case you need to be sure that the frontier orbitals are enough to discribe your system. There are even some softwares that can help you in this process, e.g, http://link.springer.com/article/10.1007%2Fs00894-014-2492-1 and http://www.sg-chem.net/aomix/.
Mulliken population analysis is not good, because it lacks any physical or mathematical limits as the basis set is improved towards completeness.
Here are some things you should keep in mind when choosing a method to compute the partial atomic charges:
Net atomic charges, also called partial charges or partial atomic charges, are commonly used for two different purposes: (1) to quantify the transfer of electrons between atoms in a material as computed by quantum chemistry and (2) to construct force-fields (for classical molecular dynamics or Monte Carlo simulations) that approximately reproduce the electrostatic potential surrounding the material. While quantum chemical topology (QCT), also called quantum theory of atoms in molecules (QTAIM), often describes electron transfer in buried atoms with reasonable accuracy, the QCT atomic charges are not suitable to construct point-charge models for classical force-fields, because the QCT atomic multipoles are large in magnitude. (The QCT method can be used to construct accurate force-fields using multi-centered polyatomic multipole expansions, but these are more complicated than the simple point-charge based force-fields often used.) On the other hand, electrostatic potential derived point charges (e.g., CHELP, CHELPG, ESP, Merz-Singh-Kollman, REPEAT) have reasonable accuracy for reproducing the electrostatic potential surrounding the material, but these do not accurately describe electron transfer for buried atoms.
The density –derived electrostatic and chemical (DDEC) methods solve this problem by partitioning the electron density to simultaneously reproduce atomic chemical states and the electrostatic potential surrounding the material with excellent accuracy. The latest generation (called DDEC6) is described in these papers: (a) T. A. Manz and N. Gabaldon Limas, “Introducing DDEC6 atomic population analysis: part 1. Charge partitioning theory and methodology,” RSC Advances, 6 (2016) 47771-47801 (http://dx.doi.org/10.1039/C6RA04656H) and (b) N. Gabaldon Limas and T. A. Manz, “Introducing DDEC6 atomic population analysis: part 2. Computed results for a wide range of periodic and nonperiodic materials,” RSC Advances, 6 (2016) 45727-45747 (http://dx.doi.org/10.1039/C6RA05507A). It gives net atomic charges that are closely correlated to many experimental properties as described in those articles. The DDEC6 method is implemented in the free Chargemol program (http://ddec.sourceforge.net) which can analyze results of GAUSSIAN, VASP, and other quantum chemistry programs.
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