We present the theoretical and technical foundations of the Amsterdam Density Functional (ADF) program with a survey of the characteristics of the code (numerical integration, density fitting for the Coulomb potential, and STO basis functions). Recent developments enhance the efficiency of ADF (e.g., parallelization, near order-N scaling, QM/MM) and its functionality (e.g., NMR chemical shifts, COSMO solvent effects, ZORA relativistic method, excitation energies, frequency-dependent (hyper)polarizabilities, atomic VDD charges). In the Applications section we discuss the physical model of the electronic structure and the chemical bond, i.e., the Kohn–Sham molecular orbital (MO) theory, and illustrate the power of the Kohn–Sham MO model in conjunction with the ADF-typical fragment approach to quantitatively understand and predict chemical phenomena. We review the “Activation-strain TS interaction” (ATS) model of chemical reactivity as a conceptual framework for understanding how activation barriers of various types of (competing) reaction mechanisms arise and how they may be controlled, for example, in organic chemistry or homogeneous catalysis. Finally, we include a brief discussion of exemplary applications in the field of biochemistry (structure and bonding of DNA) and of time-dependent density functional theory (TDDFT) to indicate how this development further reinforces the ADF tools for the analysis of chemical phenomena. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 931–967, 2001

Chemistry with ADF

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

The quantum mechanics of proper open systems yields the physics that governs the local behavior of the electron density, ρ(r). The Ehrenfest force F(r) acting on an element of ρ(r) and the virial field ν(r) that determine its potential energy are obtained from equations of motion for the electronic momentum and virial operators, respectively. Each is represented by a “dressed” density, a distribution in real space that results from replacing the property in question for a single electron with a corresponding density that describes its average interaction with all of the remaining particles in the system. All bond paths, lines of maximum density linking neighboring nuclei in a system in stable electrostatic equilibrium, have a common physical origin in terms of F(r) and ν(r), regardless of the nature of the interaction. Each is homeomorphically mirrored by a virial path, a line of maximally negative potential energy density linking the same nuclei. The presence of a bond path and its associated virial path...

A Bond Path: A Universal Indicator of Bonded Interactions

An extended semiempirical tight-binding model is presented, which is primarily designed for the fast calculation of structures and noncovalent interaction energies for molecular systems with roughly 1000 atoms. The essential novelty in this so-called GFN2-xTB method is the inclusion of anisotropic second order density fluctuation effects via short-range damped interactions of cumulative atomic multipole moments. Without noticeable increase in the computational demands, this results in a less empirical and overall more physically sound method, which does not require any classical halogen or hydrogen bonding corrections and which relies solely on global and element-specific parameters (available up to radon, Z = 86). Moreover, the atomic partial charge dependent D4 London dispersion model is incorporated self-consistently, which can be naturally obtained in a tight-binding picture from second order density fluctuations. Fully analytical and numerically precise gradients (nuclear forces) are implemented. The...

GFN2-xTB-An Accurate and Broadly Parametrized Self-Consistent Tight-Binding Quantum Chemical Method with Multipole Electrostatics and Density-Dependent Dispersion Contributions.

In the past 30 years, Kohn–Sham density functional theory has emerged as the most popular electronic structure method in computational chemistry. To assess the ever-increasing number of approximate...

Thirty years of density functional theory in computational chemistry: an overview and extensive assessment of 200 density functionals

PBE1PBE/6-311+G(d,p) computations exploring the microsolvation of neutral and zwitterionic glycine are reported. A broad configuration search was performed to identify the lowest energy clusters of glycine with one to seven water molecules. The structures of the clusters are analyzed on the basis of the hydrogen-bonding network established between the water molecules and between water and glycine. Neutral glycine is favored when associated with zero to six water molecules, but with seven water molecules the two structures are isoenergetic.

Microsolvation of glycine: a DFT study.

Twenty-three organolithium compounds were analyzed by using the topological theory of molecular structure. The geometry of each compound was first optimized, making use of the 3-21G basis set. Then integrated lithium charges and quantities characterizing the carbon-lithium bond critical point, such as rho/sub c/ (C-Li), del/sup 2/rho/sub c/(C-Li), and the local energy density, were calculated. The results confirm the nature of the carbon-lithium bond to be primarily ionic. Bond path networks of these compounds were also calculated and proved surprising. Coordination numbers of lithium, as assigned by the topological theory, range from one to four. Similarly defined coordination numbers of carbon range as high as nine. Unexpectedly, some putatively bridging lithiums are not bridging in a topological sense. Additional unexpected features of the bond path networks are bond paths connecting essentially neutral carbons with lithiums and bond paths connecting highly negatively charged carbons that are widely separated. No lithium-lithium bond paths are found. Finally, unstable topological structures occur at potential energy minima. Polarization of electrons toward what are essentially lithium cations accounts for the carbon-lithium bond paths observed.

Bond paths and bond properties of carbon-lithium bonds

Computation of the ring strain energy of 1,1-dimethylcyclobutane with a variety of methods reveals that there is no significant enthalpic component of the gem-dimethyl effect as measured by the ring strain energy.

The gem-Dimethyl Effect Revisited

Electronic publication has changed the relationship between publisher and scientist. This Policy Forum argues, because Federally-supported science is a public good, that authors of works based on such support should retain copyright, and issue licenses to their publishers.

Who Should Own Scientific Papers

Nucelophilic substitution at selenium is examined using the B3LYP and MP2 methods. Various nucleophiles (HS-, CH3S-, HSe-, and CH3Se-) and substrates (R1SSeR2 and R1SeSeR2 with R1 and R2 = H or Me) are used to model substitution at selenium in diselenides and selenosulfides. In all cases, the mechanism is addition−elimination. A stable hypercoordinate selenium intermediate lies in a well that is 8−14 kcal mol-1 deep. Nucleophilic attack at selenium is both kinetically and thermodynamically more favorable than at sulfur.

Steven M. Bachrach

Papers

Microsolvation of glycine: a DFT study.

Bond paths and bond properties of carbon-lithium bonds

The gem-Dimethyl Effect Revisited

Who Should Own Scientific Papers

Nucleophilic attack at selenium in diselenides and selenosulfides. A computational study