An extended PCILO method

The perturbative configuration interaction using strictly localized molecular orbitals, called the modified PCILO method has been applied in this communication for the calculations of the energy terms of 15 small molecules up to the third order of the perturbation theory. For this method the use of the Rayleigh-Schrodinger many-body perturbation theory with the Moller-Plesset type of the Hamiltonian partitioning is characteristic. On the CNDO/2 and INDO level of approximations the strictly localized molecular orbitals have been constructed by solving the modified 2 x 2 Roothaan's equations. From the zeroth order ground-state wave function the charge distributions, dipole moments and carbon 13-proton nuclear spin-spin coupling constants have been calculated. Results show that the chemical formula, represented with the zeroth order of the perturbation theory, is a good order of the approximation for the study of the molecule. For diatomic molecules the equilibrium interatomic distances and harmonic force constants have been calculated up to the third order of the perturbation theory. The second order of the perturbation theory provides results which are very near to the MO-LCAO-SCF calculations. The main advantage of the PCILO method lies in much saving of the computing time.

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PCILO study of hydrogen bond and proton transfer in systems 1-methylthymine-acetamide and 1-methylthymine-acetic acid

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19810957 ◽

1981 ◽

Vol 46 (4) ◽

pp. 957-962 ◽

Cited By ~ 1

Author(s):

Milan Remko

Keyword(s):

Hydrogen Bond ◽

Acetic Acid ◽

Hydrogen Bonds ◽

Proton Transfer ◽

Quantum Chemical ◽

Potential Functions ◽

Double Proton Transfer ◽

Proton Potential ◽

Pcilo Method

Complexes containing two hydrogen bonds of the systems 1-methylthymine-acetamide and 1-methylthymine-acetic acid have been studied by the quantum-chemical PCILO method. In accordance with experiment our PCILO calculations have shown that acetic acid forms stronger hydrogen bonds than acetamide with 1-methylthymine. Further the PCILO method has been used to study of double proton transfer in O-H...O and N-H...O bonds of the complexes 1-methylthymine-acetamide and 1-methylthymine-acetic acid. Using equilibrium O...O and N...O distances, the PCILO calculations have given one-minimum proton potential functions. The proton transfer has not been observed. At somewhat longer N...O and O...O distances (0.30 nm) the PCILO calculations indicate a second minimum as a shoulder.

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Preferred conformers in 3-aminopropanol by the PCILO method

Journal of Chemical Sciences ◽

10.1007/bf02879397 ◽

1981 ◽

Vol 90 (4) ◽

Author(s):

Anil Saran ◽

M M Dhingra

Keyword(s):

Pcilo Method

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Calculation of stabilization energy of parallel hexane molecules

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19823004 ◽

1982 ◽

Vol 47 (11) ◽

pp. 3004-3012

Author(s):

Ján Gajdoš ◽

Tomáš Bleha

Keyword(s):

Quantum Chemical ◽

Molecular Crystals ◽

Stabilization Energy ◽

Chemical Methods ◽

Quantum Chemical Methods ◽

Pcilo Method ◽

Stabilization Energies ◽

Energy Determination ◽

Rotational Freedom ◽

Calculation Procedures

Molecular-mechanics method has been used for calculation od stable configurations of n-hexane pairs and triads in extended all-trans conformations with full translational and rotational freedom of the molecules during optimization. The calculated stabilization energies and equilibrium distances have been compared with the experimental data obtained for molecular crystals of paraffins. The comparison enables to distinguish the effects characteristical of the collective packing forces in the crystal. The optimum configurations of some hexane pairs have also been calculated by the quantum-chemical PCILO method. The results indicate superiority of MMC to the quantum-chemical methods and other empirical calculation procedures for the purposes of the stabilization energy determination.

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