Quantum chemical software package

Even if a quantum chemical software package does not feature an implementation of a given static response property, it is often possible to evaluate the property as an energy derivative by finite difference. Most packages allow the addition of external static fields to the Hamiltonian, making it possible to compute the energy at a specified field strength, (F). From the definition of the partial derivative, we may thus compute the dipole moment and polarizability from finite difference formulas such as... 

The appropriate choice of multi-reference function for quasi-degenerate problems is a significant problem and one which we do not address here. The use of a multireference formalism is required for problems as simple as the dissociation of the ground state of the hydrogen molecule. The choice of multi-reference function is dictated by the physics and chemistry of the systems under study. For more complicated problems the choice of reference requires considerable care. This choice certainly represents a significant barrier to the development of black box quantum chemical software packages for problems demanding the use of a multi-reference formalism. 

Zemer and co-workers had subsequently attempted to use RPA as an alternative to Singles Cl for computing molecular electronic spectra with ZINDO code. " However, historically, these early RPA advances did not develop into standard quantum chemical software. Modern computational packages " usually offer extensive Cl codes but not propagator-based techniques for handling the electronic correlations. However, current studies of propagator techniques - will be gradually incorporated into quantum-chemical software. 

Equation (2) was also used to calculate quantum chemical approach. On the basis of previous results [19], calculated electrostatic potentials were computed from ab initio wave functions obtained in the framework of the HF/SCF method using a split-valence basis set (3-21G) and a split-valence basis set plus polarisation functions on atoms other than hydrogen (6-31G ). The GAUSSIAN 90 software package [20] was used. Since ab initio calculations of the molecular wave function for the whole... 

A specialized MOPAC computer software package and, in particular, its PM3 quantum-chemical program has been successfully applied in calculations. The results of calculations have shown that both oxygen atoms form bonds with two more active carbon atoms of CP molecular cluster (so-called bridge model of adsorption). The total energy of system after a chemical adsorption at such active atoms is minimal. 

Recently, quantum chemical computational techniques, such as density functional theory (DFT), have been used to study the electrode interface. Other methods ab initio methods based on Hartree-Fock (HF) theory,65 such as Mollcr-PIcsset perturbation theory,66,67 have also been used. However, DFT is much more computationally efficient than HF methods and sufficiently accurate for many applications. Use of highly accurate configuration interaction (Cl) and coupled cluster (CC) methods is prohibited by their immense computational requirements.68 Advances in computing capabilities and the availability of commercial software packages have resulted in widespread application of DFT to catalysis. 

Many software packages have been developed for calculation of molecular descriptors. Table 5.5 shows some software employed for molecular modeling, quantum-chemical calculations, molecular dynamics, and QSARs. 

For calculation of molecular models it was used quantum-chemical a method ab-initio (basis 6-31G ) from software package GAMESS version 6.0 [19], Minimization of full energy of system was carried out rpanneHTHbiM by a method with optimization of all geometrical parameters at the "frozen" coordinate of reaction. Calculation was carried out in classical approach(approximation) of an isolated molecule, a gas phase. 

Another attempt to formalize the distribution of software for atomic and molecular physics is the journal Computer Physics Communications K. V. Roberts, Comput. Phys. Commun., 1969, 1, 1 which published both scientific papers and computer programs. In spite of the continued success of this journal, it has nevertheless has to be observed that few complete quantum chemical packages have been published via this mechanism, although there are exceptions. For example, the HONDO code, The general atomic and molecular electronic structure system HONDO version 7.0 was published in Computer Physics Communications in 1989. ... 

There are two primary methods to calculate simulated spectra, theoretically and empirically. Theoretical simulations establish a molecular model based on quantum mechanical calculations, while empirical simulations rely on a database of experimentally measured chemical shifts and coupling constants for known structures. There are a number of software programs available for either simulation method. Some software packages simulate only 1-D proton and carbon spectra, while others include additional analytical simulations, such as 2-D NMR, HPLC retention times, log P, log D, etc. 

Quantum-chemical calculations were carried out using the LabVision Software Package on a Silicon Graphics Iris Indigo workstation. The molecular orbital semiempirical method was performed using the AMI Hamiltonian. 

All these cluster models were initially optimised using CVFF potentials provided in the BIOSYM software package to improve the computational efficiency of the quantum chemical optimization. 

It was at this juncture that Becke started a series of publications on Density functional thermochemistry [9-13]. The title publication on the role of exact exchange is the third paper in this series [11] and has had an astonishing impact on the entire field of quantum chemistry. One clear measure of the impact of this 1993 paper is that it has already accumulated more than 2200 citations in the scientific literature in less than 6 years [14]. Interestingly, most of the citations are from practitioners of quantum chemistry who have investigated a variety of chemical applications using functionals such as B3LYP with commercial software packages. 

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