Density Functional Calculations of E2 and SN2 Reactions: Effects of the Choice of Density Functional, Basis Set, and Self-Consistent Iterations

2010 ◽  
Vol 6 (4) ◽  
pp. 1104-1108 ◽  
Author(s):  
Yan Zhao ◽  
Donald G. Truhlar
Keyword(s):  
Density Functional Calculations ◽  
Density Functional ◽  
Basis Set ◽  
Functional Basis ◽  
Sn2 Reactions ◽  
Self Consistent

scholarly journals Study of odd–even effects in physisorption and chemisorption of Ar, N2, O2 and NO on open shell Ag11–13+ clusters by means of self-consistent van der Waals density functional calculations

2019 ◽  
Vol 21 (45) ◽  
pp. 25158-25174
Author(s):  
Eva M. Fernández ◽  
Luis C. Balbás
Keyword(s):  
Small Molecules ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Van Der Waals ◽  
Open Shell ◽  
Self Consistent

Electronic and structural odd-even effects in the adsorption of small molecules on open shell silver cationic clusters have been rationalized.

Adhesion In NiAl-Cr From First Principles

1995 ◽  
Vol 409 ◽  
Author(s):  
James E. Raynolds ◽  
John R. Smith ◽  
David J. Srolovitz ◽  
G.-L. Zhao
Keyword(s):  
First Principles ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Interfacial Stress ◽  
Work Of Adhesion ◽  
Separation Curve ◽  
Self Consistent

AbstractWe have calculated the work of adhesion (i.e. energy for rigid fracture) and peak interfacial stress for NiAl, Cr, and NiAl–Cr using self-consistent density functional calculations to obtain the complete energy vs. separation curve for each system. Our calculations indicate that the work of adhesion is largest for Cr and smallest for NiAI while those for interfaces of NiAI with Cr are intermediate. We have also estimated that segregation processes could alter the work of adhesion for the AlNi/Cr interface by up to 20% since Al tends to segregate to the free NiAl surface while Ni tends to segregate to the AlNi/Cr interface.

The Beijing Density Functional (BDF) Program Package: Methodologies and Applications

2003 ◽  
Vol 02 (02) ◽  
pp. 257-272 ◽  
Author(s):  
Wenjian Liu ◽  
Fan Wang ◽  
Lemin Li
Keyword(s):  
Density Functional Calculations ◽  
Density Functional ◽  
Program Package ◽  
Basis Set ◽  
Molecular Systems ◽  
Technical Issues

The Beijing Density Functional (BDF) program package is such a code that can perform nonrelativistic, one-, two-, and four-component relativistic density functional calculations on medium-sized molecular systems with various functionals in most compact and yet sufficient basis set expansions. The mergence of different approaches in a single code facilitates direct and systematic comparisons between different Hamiltonians, since they share all the same numerical and technical issues. In this account, the methodologies adopted in the code will be discussed in great detail and some applications of the code will be briefly presented.

A Robust Non-Self-Consistent Tight-Binding Quantum Chemistry Method for large Molecules

2019 ◽  
Author(s):  
Philipp Pracht ◽  
Eike Caldeweyher ◽  
Sebastian Ehlert ◽  
Stefan Grimme
Keyword(s):  
Density Functional ◽  
Tight Binding ◽  
Computational Cost ◽  
Vibrational Frequencies ◽  
Molecular Structures ◽  
New Method ◽  
Basis Set ◽  
Semiempirical Methods ◽  
Electronic Interaction ◽  
Self Consistent

We propose a semiempirical quantum chemical method, designed for the fast calculation of molecular Geometries, vibrational Frequencies and Non-covalent interaction energies (GFN) of systems with up to a few thousand atoms. Like its predecessors GFN-xTB and GFN2-xTB, the new method termed GFN0-xTB is parameterized for all elements up to radon (Z = 86) and mostly shares well-known density functional tight-binding approximations as well as basis set and integral approximations. The main new feature is the avoidance of the self-consistent charge iterations leading to speed-ups of a factor of 2-20 depending on the size and electronic complexity of the system. This is achieved by including only quantum mechanical contributions up to first-order which are incorporated similar to the previous versions without any pair-specific parameterization. The essential electrostatic electronic interaction is treated by a classical electronegativity equilibration charge model yielding atomic partial charges that enter the electronic Hamiltonian indirectly. Furthermore, the atomic charge-dependent D4 dispersion correction is included to account for long range London correlation effects. Formulas for analytical total energy gradients with respect to nuclear displacements are derived and implemented in the <i>xtb </i>code allowing numerically very precise structure optimizations. The neglect of self-consistent energy terms not only leads to a large gain in computational speed but also can increase robustness in electronically difficult situations because ill-convergence or artificial charge-transfer (CT) is avoided. The comparison of GFN0-xTB and GFN/GFN2-xTB allows dissection of quantum electronic polarization and CT effects thereby improving our understanding of chemical bonding. Compared to the most sophisticated multipole-based GFN2-xTB model (which approaches DFT accuracy for the target properties closely), GFN0-xTB performs slightly worse for non-covalent interactions and molecular structures, while very good results are observed for conformational energies. Vibrational frequencies are obtained less accurately than with GFN/GFN2-xTB but they may still be useful for various purposes like estimating relative thermostatistical reaction energies. Most exceptional is the fact that even relatively complicated transition metal complex structures can be accurately optimized with a non-self-consistent quantum approach. The new method bridges the gap between force-fields and traditional semiempirical methods with its excellent computational cost to accuracy ratio and is intended to explore the chemical space of large molecular systems and solids.<br>

A Robust Non-Self-Consistent Tight-Binding Quantum Chemistry Method for large Molecules

2019 ◽  
Author(s):  
Philipp Pracht ◽  
Eike Caldeweyher ◽  
Sebastian Ehlert ◽  
Stefan Grimme
Keyword(s):  
Density Functional ◽  
Tight Binding ◽  
Computational Cost ◽  
Vibrational Frequencies ◽  
Molecular Structures ◽  
New Method ◽  
Basis Set ◽  
Semiempirical Methods ◽  
Electronic Interaction ◽  
Self Consistent

We propose a semiempirical quantum chemical method, designed for the fast calculation of molecular Geometries, vibrational Frequencies and Non-covalent interaction energies (GFN) of systems with up to a few thousand atoms. Like its predecessors GFN-xTB and GFN2-xTB, the new method termed GFN0-xTB is parameterized for all elements up to radon (Z = 86) and mostly shares well-known density functional tight-binding approximations as well as basis set and integral approximations. The main new feature is the avoidance of the self-consistent charge iterations leading to speed-ups of a factor of 2-20 depending on the size and electronic complexity of the system. This is achieved by including only quantum mechanical contributions up to first-order which are incorporated similar to the previous versions without any pair-specific parameterization. The essential electrostatic electronic interaction is treated by a classical electronegativity equilibration charge model yielding atomic partial charges that enter the electronic Hamiltonian indirectly. Furthermore, the atomic charge-dependent D4 dispersion correction is included to account for long range London correlation effects. Formulas for analytical total energy gradients with respect to nuclear displacements are derived and implemented in the <i>xtb </i>code allowing numerically very precise structure optimizations. The neglect of self-consistent energy terms not only leads to a large gain in computational speed but also can increase robustness in electronically difficult situations because ill-convergence or artificial charge-transfer (CT) is avoided. The comparison of GFN0-xTB and GFN/GFN2-xTB allows dissection of quantum electronic polarization and CT effects thereby improving our understanding of chemical bonding. Compared to the most sophisticated multipole-based GFN2-xTB model (which approaches DFT accuracy for the target properties closely), GFN0-xTB performs slightly worse for non-covalent interactions and molecular structures, while very good results are observed for conformational energies. Vibrational frequencies are obtained less accurately than with GFN/GFN2-xTB but they may still be useful for various purposes like estimating relative thermostatistical reaction energies. Most exceptional is the fact that even relatively complicated transition metal complex structures can be accurately optimized with a non-self-consistent quantum approach. The new method bridges the gap between force-fields and traditional semiempirical methods with its excellent computational cost to accuracy ratio and is intended to explore the chemical space of large molecular systems and solids.<br>

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