We present a trust-region augmented Hessian implementation (TRAH-SCF) for restricted and unrestricted Hartree-Fock Kohn-Sham methods. With TRAH-SCF convergence can always be achieved with tight thresholds, which requires just modest number of iterations. Our benchmark study our illustrative applications focus on open-shell molecules, also antiferromagnetically coupled systems, it is notoriously...

The calculation of molecular response properties in dynamic molecular systems is a major challenge that requires sampling over many steps of, e.g., Born-Oppenheimer molecular dynamics (BO-MD) simulations. We present an extrapolation scheme to accelerate such calculations for multiple steps within BO-MD trajectories or equivalently within other sampling methods of conformational space. The extra...

The Kohn-Sham equation in first-principles density functional theory (DFT) calculations is a nonlinear eigenvalue problem. Solving the nonlinear eigenproblem is usually the most expensive part in DFT calculations. Sparse iterative diagonalization methods that compute explicit eigenvectors can quickly become prohibitive for large scale problems. The Chebyshevfiltered subspace iteration (CheFSI) ...

We present ab initio Hartree-Fock calculations of electric field gradients, which are related to experimental determinations of nuclear quadrupole coupling constants. The nucleus of special interest is 1 7 0 but other nuclei in the molecules, especially N, 2 H and 3 3 S are included. The calculations were performed (a) as single molecules either at the SCF and MP2 correlated levels, (b) as clus...

Analytic gradients of dual-basis Hartree-Fock and density functional theory energies have been derived and implemented, which provide the opportunity for capturing large basis-set gradient effects at reduced cost. Suggested pairings for gradient calculations are 6-31G/6-31G**, dual[-f,-d]/cc-pVTZ, and 6-311G*/6-311 + +G(3df,3pd). Equilibrium geometries are produced within 0.0005 A of large-basi...

The power of density functional theory is often limited by the high computational demand in solving an eigenvalue problem at each self-consistent-field (SCF) iteration. The method presented in this paper replaces the explicit eigenvalue calculations by an approximation of the wanted invariant subspace, obtained with the help of well-selected Chebyshev polynomial filters. In this approach, only ...

The power of density functional theory is often limited by the high computational demand in solving an eigenvalue problem at each self-consistent-field (SCF) iteration. The method presented in this paper replaces the explicit eigenvalue calculations by an approximation of the wanted invariant subspace, obtained with the help of well-selected Chebyshev polynomial filters. In this approach, only ...

Born-Oppenheimer molecular dynamics calculations, especially those that exploit information retained from previous time steps in order to accelerate convergence of the electronic structure calculations, can suffer from systematic error in the energy gradient that manifests as a drift in the microcanonical energy. Here, we demonstrate that this is only the case when the self-consistent field (SC...