scholarly journals The Use of Quantum Chemical Semiempirical Methods to Calculate the Lattice Energies of Organic Molecular Crystals. Part I: The Three Polymorphs of Glycine

2000 ◽  
Vol 55 (6-7) ◽  
pp. 609-615 ◽  
Author(s):  
Gerhard Raabe
Keyword(s):  
Quantum Chemical ◽  
Chemical Method ◽  
Molecular Crystals ◽  
Lattice Energy ◽  
Potential Method ◽  
Electrostatic Energy ◽  
Semiempirical Methods ◽  
Quantum Chemical Method ◽  
Organic Molecular Crystals ◽  
Lattice Energies

Abstract A method to calculate the lattice energies of organic molecular crystals is described. It is based on the semiempirical quantum chemical MINDO/3 approximation but might also be used within the framework of any other quantum chemical method. The lattice energy is approximated by the sum of dispersion-, induction-, exchange repulsion-, and electrostatic energy. Different, however, from other schemes employed in this field, like for example the atom-atom-potential method, the variables in the expression for the lattice energy have not been fitted to reproduce experimental values and, therefore, the single contributions retain their original physical meaning. Moreover, the method offers the advantage that it may be directly applied to all compounds that can be treated within the framework of the underlying quantum chemical method. Thus, time consuming readjustment of the entire parameter set upon extension of the group of target molecules by another class of compounds becomes obsolete. As an example, the lattice energies of the three polymorphs of glycine are calculated.

scholarly journals The Use of Quantum-Chemical Semiempirical Methods to Calculate the Lattice Energies of Organic Molecular Crystals. Part III: The Lattice Energy of Borazine (B3N3H6) and its Packing in the Solid State*

2004 ◽  
Vol 59 (9) ◽  
pp. 609-614 ◽  
Author(s):  
Gerhard Raabe
Keyword(s):  
Quantum Chemical ◽  
Lattice Energy ◽  
Low Pressure ◽  
Semiempirical Methods ◽  
Dispersion Energy ◽  
Organic Molecular Crystals ◽  
Ab Initio Theory ◽  
Lower Melting Point ◽  
Chemical Scheme ◽  
Lattice Energies

A previously presented quantum-chemical scheme has been used to calculate the lattice energies of borazine (B3N3H6), the low pressure polymorph of benzene (C6H6), and of borazine in the lowpressure benzene lattice utilizing some frequently used semiempirical methods (CNDO/2, INDO, MINDO/3, MNDO, AM1, PM3, MSINDO). With all methods the lattice energy of the title compound was found to be less favourable than that of isoelectronic benzene, which offers an explanation of the significantly lower melting point of B3N3H6. Calculation of the lattice energy of borazine in the crystal lattice of the low-pressure modification of benzene revealed that the interactions between the molecules in this environment are not so stabilizing as those in its own lattice. This is predominantly due to a less favourable contribution of the dispersion energy. The semiempirical results have qualitatively been confirmed by quantum-chemical calculations on small molecular clusters at the MP2/6-31+G*//HF/6-31+G* level of ab initio theory. In these calculations we assumed pairwise additivity of the intermolecular interactions and calculated the energy of interaction between a reference molecule and all those neighbours to which the shortest intermolecular distance does not exceed 3Å.

scholarly journals The Use of Quantum-Chemical Semiempirical Methods to Calculate the Lattice Energies of Organic Molecular Crystals. Part II: The Lattice Energies of α- and β-Oxalic Acid (COOH)2

2002 ◽  
Vol 57 (12) ◽  
pp. 961-966 ◽  
Author(s):  
Gerhard Raabe
Keyword(s):  
Oxalic Acid ◽  
Quantum Chemical ◽  
Lattice Energy ◽  
Energy Difference ◽  
Electrostatic Energy ◽  
Semiempirical Methods ◽  
Stable Form ◽  
Crystal Lattices ◽  
Lattice Energies ◽  
Chemical Procedure

The lattice energies (ΔE lat) of α- and β-oxalic acid ((COOH)2) have been calculated using a recently introduced semiempirical quantum-chemical procedure. Within the framework of this method the lattice energy (ΔE lat) is evaluated as the sum of the semiempirically calculated intermolecular dispersion (ΔEdis), induction (ΔEind), repulsion (ΔErep), and electrostatic energy (ΔEels). The lattice energies of the two polymorphs of oxalic acid obtained in this way correlate not only with the results of other calculations but also with the experimentally determined heats of sublimation in that the α-modification, which has a somewhat higher heat of sublimation, is slightly more stable than the β-polymorph. However, additional quantum-chemical calculations at the non-empirical ab initio level (e. g. ZPE+MP2(FC)/6-311++G**//MP2(FC)/6-311++G**) revealed that the absolute values of the lattice energies and the heats of sublimation are not directly comparable to each other because the structures of the (COOH)2 molecules in the crystal lattices of both polymorphs differ significantly from that of the most stable form of the free molecule in the gasphase. At about 4.3 kcal/mol the calculated energy difference between the structure of the molecule in the solid state and the energetically most favourable conformation of the free (COOH)2 molecule in the gasphase is much smaller than that in the recently described case of α-glycine (28±2 kcal/mol). However, even such a small difference might be the source of serious problems if the heats of sublimation are employed to fit parameters to be used in the optimization of crystal packings.

scholarly journals Quantum-Chemical Quasi-Docking for Molecular Dynamics Calculations

Nanomaterials ◽  
2022 ◽  
Vol 12 (2) ◽  
pp. 274
Author(s):  
Alexey Sulimov ◽  
Danil Kutov ◽  
Ivan Ilin ◽  
Vladimir Sulimov
Keyword(s):  
Quantum Chemical ◽  
Chemical Method ◽  
Wide Spectrum ◽  
Semiempirical Methods ◽  
Implicit Solvent ◽  
Quantum Chemical Method ◽  
Dispersion Interactions ◽  
Ligand Complex ◽  
High Quality Protein ◽  
Solvent Model

The quantum quasi-docking procedure is used to compare the docking accuracies of two quantum-chemical semiempirical methods, namely, PM6-D3H4X and PM7. Quantum quasi-docking is an approximation to quantum docking. In quantum docking, it is necessary to search directly for the global minimum of the energy of the protein-ligand complex calculated by the quantum-chemical method. In quantum quasi-docking, firstly, we look for a wide spectrum of low-energy minima, calculated using the MMFF94 force field, and secondly, we recalculate the energies of all these minima using the quantum-chemical method, and among these recalculated energies we determine the lowest energy and the corresponding ligand position. Both PM6-D3H4X and PM7 are novel methods that describe well-dispersion interactions, hydrogen and halogen bonds. The PM6-D3H4X and PM7 methods are used with the COSMO implicit solvent model as it is implemented in the MOPAC program. The comparison is made for 25 high quality protein-ligand complexes. Firstly, the docking positioning accuracies have been compared, and we demonstrated that PM7+COSMO provides better positioning accuracy than PM6-D3H4X. Secondly, we found that PM7+COSMO demonstrates a much higher correlation between the calculated and measured protein–ligand binding enthalpies than PM6-D3H4X. For future quantum docking PM7+COSMO is preferable, but the COSMO model must be improved.

Solvation of ions by dipolar aprotic solvents and water. A CNDO/2 study

1985 ◽  
Vol 50 (11) ◽  
pp. 2493-2508 ◽  
Author(s):  
Petr Kyselka ◽  
Zdeněk Havlas ◽  
Ivo Sláma
Keyword(s):  
Binary Mixtures ◽  
Quantum Chemical ◽  
Chemical Method ◽  
Molecular Structures ◽  
Dimethyl Sulphoxide ◽  
Ternary Mixtures ◽  
Aprotic Solvents ◽  
Quantum Chemical Method ◽  
Solvation Of Ions ◽  
Dipolar Aprotic Solvents

Solvation of Li+, Be2+, Na+, Mg2+, and Al3+ ions has been studied in binary mixtures with dimethyl sulphoxide, dimethylformamide, acetonitrile and water, and in ternary mixtures of the organic solvents with water. The CNDO/2 quantum chemical method was used to calculate the energies of solvation, molecular structures and charge distributions for the complexes acetonitrile...ion (1:1, 2:1, 4:1), dimethyl sulphoxide...ion (1:1), dimethylformamide...ion (1:1), and acetonitrile (dimethyl sulphoxide, dimethylformamide)...ion...water (1:1:1).

The optoelectronic properties of π-conjugated organic molecules based on terphenyl and pyrrole for BHJ solar cells: DFT / TD-DFT theoretical study

2021 ◽  
Vol 10 (4) ◽  
pp. 489-502 ◽  
Author(s):  
M. Raftani ◽  
T. Abram ◽  
W. Loued ◽  
R. Kacimi ◽  
A. Azaid ◽  
...  
Keyword(s):  
Solar Cells ◽  
Quantum Chemical ◽  
Chemical Method ◽  
Chemical Reactivity ◽  
Optoelectronic Properties ◽  
Oscillator Strengths ◽  
Frontier Molecular Orbital ◽  
Bandgap Energy ◽  
Quantum Chemical Method ◽  
Td Dft

In the present paper, four π-conjugated materials, based on terphenyl and pyrrole, with A–D–A structure have been theoretically studied to propose new organic compounds to be used in the organic solar cell field. Moreover, the geometrical and optoelectronic properties of the designed molecules M1, M2, M3 and M4 have been computed after optimization in their fundamental states, using the quantum chemical method DFT / B3LYP/ 6−311G (d, p). Different parameters including HOMO and LUMO energy levels, bandgap energy, frontier molecular orbital (FMO), chemical reactivity indices, the density of states (DOS), Voc, electrostatic potential (ESP), and thermodynamic parameters at several temperatures in the range of 0-500 K have been determined. The absorption properties including the transition energy, the wavelengths (λmax), the excitation vertical energy, and the corresponding oscillator strengths of these molecules have been studied using the quantum chemical method TD−DFT / CAM–B3LYP / 6–311G (d, p). The obtained results of our studied compounds show that M3 (with 2H, 2'H-1, 1'-biisoindole moiety) as a donor group has special optoelectronic, absorption, and good photovoltaic characteristics. Thus, they can be utilized as an electron-donating in organic solar cells BHJ type.

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