The conformational preferences of the lignin guaiacyl structural unit were studied by several quantitative chemistry calculation methods using vanillin as a model compound. The potential energy surfaces of the vanillin molecule were scanned by the methods of HF and DFT to find the most stable conformation, as well as three local minimum conformations and six transient conformations. Bonds stren...

The analytical energy gradient of the normalized elimination of the small component (NESC) method is derived for the first time and implemented for the routine calculation of NESC geometries and other first order molecular properties. Essential for the derivation is the correct calculation of the transformation matrix U relating the small component to the pseudolarge component of the wavefuncti...

a Nearly Tridiagonal Matrix Magdy Tawfik Hanna1 ABSTRACT A fully-fledged definition for the fractional discrete Fourier transform of type IV (FDFT-IV) is presented and shown to outperform the simple definition of the FDFT-IV which is proved to be just a linear combination of the signal, its DFT-IV and their flipped versions. This definition heavily depends on the availability of orthonormal eig...

The novel methods for binary discrete Fourier transform (DFT) computation over the finite field have been proposed. are based on a trace calculation and use cyclotomic DFT. direct DFT computational complexity has reduced due to using function functions of which stored in small tables. inverse representation elements with respect normal basis. proposed can be used encoding/decoding subfield subc...

The term electronegativity .was introduced by Linus Pauling, who characterized on the basis ofthermodynamic data from the energies of the single bonds. In present study, the Density Functional Theory(DFT) was used to calculate electronegativity of atoms. The base of calculation is similar to Pauling andMulliken methods. The results indicate that the largest value of electronegativity for Fluori...

A calculation method for Henry constants of diatomic molecules in zeolite cages is proposed. The method is based on a molecular electrostatic potential approximation formulated within a density functional theory (DFT) context for the evaluation of interaction energies. This approach is compared with ab initio and “molecule-in-point-charge-field” calculations. The effect of wave function versus ...

The performance of different DFT ~UDFT-IGLO, UDFT-GIAO, SOS-DFPT-IGLO! and hybrid-DFT approaches, as well as of HF-GIAO and MP2-GIAO methods has been compared for the calculation of O chemical shielding in the series of tetrahedral d oxo complexes MO4~M5Fe,Ru,Os!, MO4 ~M5Mn,Tc,Re!, and MO4 ~M5Cr,Mo,W!. While HF-GIAO and MP2-GIAO fail for systems with low-lying excited states ~e.g., MnO4 , CrO4 ...

We have used computational quantum chemistry to investigate the thermochemistry of α-hydrogen abstraction from the full set of amino acids normally found in proteins, as well as their peptide forms, by •OH and •SH radicals. These reactions, with their reasonable complexity in the electronic structure (at the α-carbon), are chosen as a consistent set of models for conducting a fairly robust asse...

We implement a method to study transport in a basis of many-body molecular states using the nonequilibrium Hubbard Green's function technique. A well-studied system, a junction consisting of benzene-dithiol on gold, is the focus of our consideration. Electronic structure calculations are carried out at the Hartree-Fock (HF), density functional theory (DFT), and coupled-cluster singles and doubl...

Grating displacement measurement technique is an important means to achieve precise displacement measurement of nanometer scale. Moiré fringe phase difference measurement is the basis of grating displacement measurement technique. Traditional Moiré fringe subdivision method based on DFT algorithm has low frequency resolution relatively when extracting Moiré fringe fundamental frequency spectral...