Implementation of reaction field methods in quantum chemistry computer codes

1995 ◽  
Vol 16 (1) ◽  
pp. 37-55 ◽  
Author(s):  
A. H. De Vries ◽  
P. Th. Van Duijnen ◽  
A. H. Juffer ◽  
J. A. C. Rullmann ◽  
J. P. Dijkman ◽  
...  
Keyword(s):  
Quantum Chemistry ◽  
Field Methods ◽  
Reaction Field ◽  
Computer Codes

Implementation of reaction field methods in quantum chemistry computer codes

1995 ◽  
Vol 16 (11) ◽  
pp. 1445-1446 ◽  
Author(s):  
A. H. De Vries ◽  
P. Th. Van Duijnen ◽  
A. H. Juffer ◽  
J. A. C. Rullmann ◽  
J. P. Dijkman ◽  
...  
Keyword(s):  
Quantum Chemistry ◽  
Field Methods ◽  
Reaction Field ◽  
Computer Codes

Probing Detonation Physics and Chemistry Using Molecular Dynamics and Quantum Chemistry Techniques

1995 ◽  
Vol 418 ◽  
Author(s):  
M. D. Cook ◽  
J. Fellows ◽  
P. J. Haskins
Keyword(s):  
Molecular Dynamics ◽  
Quantum Chemistry ◽  
Energetic Materials ◽  
Molecular Level ◽  
Energetic Material ◽  
Macroscopic Models ◽  
Empirical Potentials ◽  
Quantum Chemistry Calculations ◽  
Molecular Dynamics Calculations ◽  
Computer Codes

AbstractModem quantum chemistry and molecular dynamics computer codes are powerful tools with which to study the physics and chemistry of energetic materials at the molecular level. Quantum chemistry calculations, on one or two energetic molecules, can give valuable information about the initial steps in their decomposition. Molecular dynamics calculations, even with empirical potentials, can yield important information about the physical processes involved in the initiation and growth of reaction of energetic materials. The combination of Molecular dynamics and quantum chemistry techniques offers the potential to probe energetic material reaction chemistry in real systems, in some detail, in the near future. Such an approach is vital if we are to be able to create new realistic macroscopic models within hydrocodes that can describe the initiation and growth of reaction in explosives. This paper gives an overview of the approach being adopted at DRA Fort Halstead to understanding energetic materials at the molecular level. In particular, the use of quantum chemistry and Molecular dynamics to help construct new macroscopic models will be discussed.

Correlation Methods

2007 ◽  
Author(s):  
Kenneth G. Dyall ◽  
Knut Faegri
Keyword(s):  
Quantum Chemistry ◽  
Time Reversal ◽  
Relativistic Quantum ◽  
Mean Field ◽  
Spin Symmetry ◽  
Nonrelativistic Quantum ◽  
Field Methods ◽  
Hartree Fock ◽  
The Mean ◽  
The Difference

It is well known from nonrelativistic quantum chemistry that mean-field methods, such as the Hartree–Fock (HF) model, provide mainly qualitative insights into the electronic structure and bonding of molecules. To obtain reliable results of “chemical accuracy” usually requires models that go beyond the mean field and account for electron correlation. There is no reason to expect that the mean-field approach should perform significantly better in this respect for the relativistic case, and so we are led to develop schemes for introducing correlation into our models for relativistic quantum chemistry. There is no fundamental change in the concept of correlation between relativistic and nonrelativistic quantum chemistry: in both cases, correlation describes the difference between a mean-field description, which forms the reference state for the correlation method, and the exact description. We can also define dynamical and nondynamical correlation in both cases. There is in fact no formal difference between a nonrelativistic spin–orbital-based formalism and a relativistic spinor-based formalism. Thus we should be able to transfer most of the schemes for post-Hartree–Fock calculations to a relativistic post-Dirac–Hartree–Fock model. Several such schemes have been implemented and applied in a range of calculations. The main technical differences to consider are those arising from having to deal with integrals that are complex, and the need to replace algorithms that exploit the nonrelativistic spin symmetry by schemes that use time-reversal and double-group symmetry. In addition to these technical differences, however, there are differences of content between relativistic and nonrelativistic methods. The division between dynamical and nondynamical correlation is complicated by the presence of the spin–orbit interaction, which creates near-degeneracies that are not present in the nonrelativistic theory. The existence of the negative-energy states of relativistic theory raise the question of whether they should be included in the correlation treatment. The first two sections of this chapter are devoted to a discussion of these issues. The main challenges in the rest of this chapter are to handle the presence of complex integrals and to exploit time-reversal symmetry.

scholarly journals Local Anesthetics Transfer Across the Membrane: Reproducing Octanol-Water Partition Coefficients by Solvent Reaction Field Methods

2021 ◽  
Vol 68 (2) ◽  
pp. 426-432
Author(s):  
Hana Kavcic ◽  
Nejc Umek ◽  
Domen Pregeljc ◽  
Neli Vintar ◽  
Janez Mavri
Keyword(s):  
Local Anesthetics ◽  
Partition Coefficients ◽  
Ph Value ◽  
Biological Membrane ◽  
Extracellular Fluid ◽  
Biological Molecules ◽  
Field Methods ◽  
Reaction Field ◽  
Drug Classes ◽  
Experimental Values

Local anesthetics are one of the most widely used drug classes in clinical practice. Like many other biological molecules, their properties are altered depending on their protonation status, which is dependent on the pH of the environment. We studied the transport energetics of seven local anesthetics from the extracellular fluid across the biological membrane to the axoplasm in order to understand the effect of pH value on their efficacy and other pharmaco-dynamic roperties. In this we applied three different methods of solvent reaction field in conjunction with quantum chemical calculations to reproduce experimental values of n-octanol/water partition coefficients for both neutral and protonated forms. Only the SMD method of Cramer and Truhlar was able to reproduce experimental partition coefficient values. The results are discussed in terms of the function of local anesthetics under physiological conditions and in the case of local acidosis.

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