Charge population analysis

LSwdin population analysis -> charge descriptors (O atomic charge) lowest unoccupied molecular orbital -> quantum-chemical descriptors lowest unoccupied molecular orbital energy -> quantum-chemical descriptors LUMO electron density on the ath atom -> charge descriptors (O net orbital charge)... 

Mulliken electronegativity - quantum-chemical descriptors Mulliken population analysis charge descriptors (O atomic charge) multicriteria decision making - chemometrics multigraph -> graph... 

Basis Population analysis Charge on Mg atom Atomic covalence ... 

Ldwdin population analysis avoids the problem of negative populations or populations greater than 2. Some quantum chemists prefer the Ldwdin approach to that of Mulliken as the charges are often closer to chemically intuitive values and are less sensitive to basis set. 

The Fenske-Hall method is a modification of crystal held theory. This is done by using a population analysis scheme, then replacing orbital interactions with point charge interactions. This has been designed for the description of inorganic metal-ligand systems. There are both parameterized and unparameterized forms of this method. 

Chemists are able to do research much more efficiently if they have a model for understanding chemistry. Population analysis is a mathematical way of partitioning a wave function or electron density into charges on the nuclei, bond orders, and other related information. These are probably the most widely used results that are not experimentally observable. 

The subscripts i and j denote two nuclei one in the QM region and one in the MM region. The atomic charges for the MM atoms are obtained by any of the techniques commonly used in MM calculations. The atomic charges for the QM atoms can be obtained by a population analysis scheme. Alternatively, there might be a sum of interactions with the QM nuclear charges plus the interaction with the electron density, which is an integral over the electron density. 

The properties available include electrostatic charges, multipoles, polarizabilities, hyperpolarizabilities, and several population analysis schemes. Frequency correction factors can be applied automatically to computed vibrational frequencies. IR intensities may be computed along with frequency calculations. 

By default, Gaussian jobs perform a Mulliken population analysis, which partitions the total charge among the atoms in the molecule. Here is the key part of output for formaldehyde ... 

The remainder of the optimization output file displays the population analysis, molecular orbitals (if requested with Pop=Reg) and atomic charges and dipole moment for the optimized structure. 

This exercise will examine other ways of computing charges other than Mulliken population analysis. Since atomic charge is not a quantum mechanical observable, all methods for computing it are necessarily arbitrary. We ll explore the relative merits of various schemes for partitioning the electron density among the atoms in a molecular system. 

The Mulliken scheme places the negative charge more or less evenly on the three carbons, and splits the positive charge among the hydrogens. Mulliken population analysis computes charges by dividing orbital overlap evenly between the two atoms involved. 

Natural population analysis is carried out in terms of localized electron-pair bonding units. Here are the charges computed by natural population analysis (the essential output is extracted) ... 

A iMuiliken population analysis foibw > ifre SCF energy results. This analysis partitions the charge on the molecule by atom. 

In Chapter 3, we studied the topic of population analysis. In population analysis, we attempt a rough-and-ready numerical division of the electron density into atom and bond regions. In Mulliken theory, the bond contributions are divided up equally between the contributing atoms, giving the net charges. The aim of the present section is to answer the questions Are there atoms in Molecules , and if so, How can they be defined . According to Bader and coworkers (Bader, 1990) the answers to both questions are affirmative, and the boundaries of these atoms are determined by a particular property of the electron density. 

Q Atomic charge (can be fractional), fitted or from population analysis... 

Following Vincent and Radom s comprehensive ab initio study (1978), Escudero et al. (1985) also performed ab initio calculations at the STO-3G level for seven 4-substituted benzenediazonium ions. For the unsubstituted benzenediazonium ion, the optimized geometries are the same as in Figure 4-1 (I). For charge density calculations another population analysis method was used (Escudero and Yanez, 1982), and this gave results different from those of Vincent and Radom. However,... 

BOPs and atomic charges by population analysis are very sensitive to changes in the MO formulation and to the approximations (e.g. CNDO, EHT), and even to small basis set changes. 

Table 9 shows the PP MO results for this interesting series of highly strained three-membered cyclic molecules. Here a detailed comparison is possible with the best results of an all-electron study, including d functions10 (also reported in Table 9). An analysis of this table reveals how all trends in population analysis, both in charges and overlap populations, are the same in the AE + d and in the simple PP calculations, with very few and very minor exceptions. PP predicts a charge donation to the aliphatic groups, while AE predicts a withdrawal, mainly due to the availability of d orbitals on sulphur, which can allocate extra electronic charge. As outlined in the general notes on population analysis (Section III.D) comparisons should be carried out on a relative basis and,...

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