Starting SCF calculations by superposition of atomic densities

Starting SCF calculations by superposition of atomic densities

We describe the procedure to start an SCF calculation of the general type from a sum of atomic electron densities, as implemented in GAMESS-UK. Although the procedure is well known for closed-shell calculations and was already suggested when the Direct SCF procedure was proposed, the general procedure is less obvious. For instance, there is no need to converge the corresponding closed-shell Har...

Modified Quantum-Statistical Calculations for Atomic Electron Densities

Parallelization of SCF calculations within Q-Chem ✩

We have incorporated MPI based parallelism with dynamic load balance into the Hartree–Fock and DFT modules of Q-Chem. A series of benchmark calculations consisting of both single point energy and gradient calculations were carried out to gauge the performance of the parallel modules. Calculations were carried out on two different parallel computers, namely a shared memory Silicon Graphics Origi...

On nonadiabatic SCF calculations of molecular properties

We argue that the dynamic extended molecular orbital (DEMO) method may be less accurate than expected because the motion of the center of mass was not properly removed prior to the SCF calculation. Under such conditions the virial theorem is a misleading indication of the accuracy of the wavefunction. The first step in any quantum–mechanical treatment of atomic and molecular systems is the sepa...

Number Theory and Atomic Densities