The Role of Efficient Programming in Theoretical Chemistry and Physics Problems

Various aspects of efficient programming of high-performance computer systemsare discussed, using an example from modern electronic structure theory. It isshown that efficient programming is indispensable in today's theoretical studies byreducing drastically involved computer time. Timings from our quantum chemicalprogram CORREL are given for several platforms ranging from Cray Y-MP EL toPC/486.Pozna

HIGH-PERFORMANCE COMPUTINGON HETEROGENEOUS SYSTEMS

A model two-processor heterogeneous computer consisting of one scalar and one vector processoris analyzed in terms of its performance. It is demonstrated that on mixed-type (scalar-vector) applicationsit is much more effective than a homogeneous environment. Various models of the job distribution areintroduced. A working implementation in the field of quantum chemistry is presented.Pozna

On the acceleration of the convergence of singular operators in Gaussian basis sets

Gaussian type wave functions do not reproduce the interparticle cusps which result in a slow convergence of the expectation values of the operators involved in calculations of the relativistic and QED energy corrections. Methods correcting this deficiency are the main topic discussed in this paper. Benchmark expectation values of the singular operators for several few-electron systems are presented

Theory and application of explicitly correlated Gaussians

The variational method complemented with the use of explicitly correlated Gaussian basis functions is one of the most powerful approaches currently used for calculating the properties of few-body systems. Despite its conceptual simplicity, the method offers great flexibility, high accuracy, and can be used to study diverse quantum systems, ranging from small atoms and molecules to light nuclei, hadrons, quantum dots, and Efimov systems. The basic theoretical foundations are discussed, recent advances in the applications of explicitly correlated Gaussians in physics and chemistry are reviewed, and the strengths and weaknesses of the explicitly correlated Gaussians approach are compared with other few-body technique

Exponentially correlated Gaussian functions in variational calculations. The EF singlet-Sigma-g-+ state of hydrogen molecule

The Born-Oppenheimer (BO) potential energy curve, the adiabatic and the relativistic corrections for the EF state of the hydrogen molecule are calculated for the internuclear distances ranging from 0.01 to 20 bohr. 600-term variational expansions of exponentially correlated Gaussian (ECG) functions are used. The BO energies and the adiabatic corrections are more accurate than previously reported and the relativistic calculations confirm existing literature values

Efficient Calculations of Dispersion Energies for Nanoscale Systems from Coupled Density Response Functions

Dispersion energies computed from coupled Kohn–Sham (CKS) dynamic density–density response functions are known to be highly accurate. At the same time, the computational algorithm is of only modest complexity compared to other accurate methods of dispersion energy calculation. We present a new implementation of this algorithm that removes several computational barriers present in current implementations and enables calculations of dispersion energies for systems with more than 200 atoms using more than 5000 basis functions. The improvements were mainly achieved by reorganizing the algorithm to minimize memory and disk usage. We present applications to two systems: the buckycatcher complex with fullerene and the vancomycin complex with a diacetyl-Lys-d-Ala-d-Ala bacterial wall precursor, both calculations performed with triple-ζ-quality basis sets. Our implementation makes it possible to use <i>ab initio</i> computed dispersion energies in popular “density functional theory plus dispersion” approaches