| Systems involving weak molecular interactions or significant amounts of electron correlation are not accurately described by semiemperical or Hartree-Fock (HF) methods; approaches that recover at least some of the electron correlation are necessary. However, most electron correlation methods require a large amount of computing resources to acquire a significant portion of the correlation energy. Parallel implementation of correlated methods on personal computers alleviates the financial cost and allows more expensive correlated methods like coupled cluster (CC) to be pursued since resources are easily expanded.;In the present work, the development methods involving electron correlation and their application to carbon-based materials are explored. First, changes are made to the existing MP2 method in Parallel Quantum Solutions (PQS) by manipulating the manner in which the exchange integrals are stored as preparation for a coupled-cluster with doubles excitation (CCD) addition to the program. An efficient network file-handling tool is also implemented to handle data storage across a set of parallel computing nodes. The tool is generic and can be used with several parallel computational techniques outside the scope of the current work. Third, calculations involving correlated methods are performed on graphene sheet systems ranging from benzene dimer to circumcoronene dimer, which is the largest graphene sheet system studied by ab initio methods to date. Since the large dispersion forces between the sheets must be studied by correlated methods, they help establish the need for efficient implementation of the MP2 method of PQS. Finally, DFT frequency scaling factors are generated for a toxic class of ubiquitous compounds known as polycyclic aromatic hydrocarbons (PAHs). Scale factors corresponding to specific molecular deformations are generated rather than producing a single scale factor for a particular basis set and DFT functional. The improved scale factors can be used to identify experimental anomalies or new compounds and to investigate the existence of PAHs in objects of the Solar System. |
