Is there any group additive rules in the calculation of electron correlation energies of long straight chain alkane molecules?

Abstract

According to the definition in the text, the correlation energy of 1s2C of carbon atoms, the primary and secondary C-H bonding electron pairs in some CH3, CH2 fragments and CH3(CH2)mCH3 (m=1-5) linear alkane molecules are calculated and analyzed. The transferability of the correlation energies of these electron pairs in the linear alkanes is investigated. The results indicate that the correlation energy of 1s2C is perfectly transferable in the respective methyl and methylene groups, while the correlation energies of the primary and secondary C-H bonding electron pairs are approximately transferable in methyl and methylene groups. The analysis of the results of group correlation energy shows that both of the correlation energies of methyl and methylene groups are transferable in these linear alkanes. The correlation energies of methylene group in CH3(CH2)mCH3 (m=1-5) molecules are slightly decreasing showing a converging trend to a "standard" methylene group in linear alkanes. The excellent fitting relationship between the total correlation energy and the number of methylene groups of the linear alkanes shows that the total correlation energy is a linear function of the number of methylene groups, which means that the total correlation energies of large linear alkanes can be reproduced and predicted by counting the numbers of methylene groups. In this way, total correlation energy of large linear alkane molecule can be approximately calculated using this simple group additive scheme with substantial saving in computational time.

Divide-and-conquer local correlation approach to the correlation energy of large molecules

“…Within this approach, non-negligible excitation amplitudes can be obtained to a very good approximation by solving the CCD equations of various subunits, each of which is made up of some occupied and virtual LMOs. 33 In this paper, our aim is to develop a simple but effective local correlation approach for performing correlation calculations on large systems, extending the ideas included in our previous works. To make this local treatment achieve linear scaling, two obstacles must be overcome: one is to develop linear scaling localization procedures or alternatives such as pseudodiagonalization to obtain LMOs of large molecules, another is to evaluate required transformed two-electron integrals in limited operations, using screening and truncation techniques.…”

Group Contribution Model for Estimate of Correlation Energies of Linear Alkyl Alcohols

“…In the discussion of group contributions of CH 2 groups in other positions, it was found that with the increase of the number m of intervening CH 2 groups in the system, all the values of E corr (CH 2 ) were decreased from C 3 H 7 OH to C 5 H 11 OH system, i.e., the longer the alkyl chain, the smaller the group contribution of the CH 2 groups at the same position in different molecules. Comparing the correlation energy of the CH 2 group in δ position connected with the terminal CH 3 group in C 5 H 11 OH molecule which is -164.16 mh with the corresponding value in C 6 H 14 molecule which is -161.11 mh, 23 it was noted that the tiny difference came from the remote effect of the HO group. Therefore, it was predicted that with the increase of the number m of methylene groups in the linear alkyl alcohol system this value approached the value of the corresponding alkane molecule, which could be considered a "standard" methylene group.…”

“…According to Eq. (4), the group contributions of methyls in CH 3 (CH 2 ) m OH (m＝1-4) systems were calculated and shown in 23 it was noted that the value of E corr (CH 3 ) in C 5 H 11 OH system which is -188.62 mh just fell in the range of the above corresponding values. Therefore, it is easily predicted that if the number m in CH 3 (CH 2 ) m OH system is large enough that the correlation energy contribution of a CH 3 group in the system will be intending to the same value as that in the corresponding alkane system.…”

“…Furthermore, to extend this strategy to homologous organic molecules, according to the transferability and molecular similarity of atomic groups, [16][17][18][19][20][21][22] we have studied the approximately transferable property of the correlation energies of methyl and methylene groups along the series of linear alkanes and developed the group additive scheme for general applicability. 23 In this paper, we analyze the variability and transferability of correlation energy contributions in terms of functional groups in CH 3 (CH 2 ) m OH (m＝0-4) linear alkyl alcohols. Despite the dependence of correlation energy contributions of CH 3 and HO polar groups on the length of chain while m is a relative small number, the value of the "standard" methylene groups still exhibits the transferable property in CH 3 (CH 2 ) m OH series.…”

Superposition-additive approach in the description of thermodynamic parameters of formation and clusterization of substituted alkanes at the air/water interface

“…The molar thermodynamic characteristics (enthalpy, entropy, Gibbs' energy) of micelle formation of non-ionic surfactants in their aqueous solution were calculated in Refs. [7][8][9]. In our studies, see e.g.…”