Mpller-Plesset perturbation theory mechanics

The next two papers (6.3 and 6.4) deal with the application of an ab initio quantum mechanical method (the Mpller-Plesset perturbation theory) to large binary clusters formed by water with methane or methanol. The molecules of methane or methanol were selected because they represent two extreme types of molecules 1) methane, an entirely hydrophobic molecule and 2) methanol, which has both hydrophobic and hydrophilic parts and, in addition, can form H-bonds with water. These calculations allow one to analyze the changes in the H-bond network of water in the vicinity of both molecules when they are inserted into pure water. These two cases might be helpful in understanding much more complex molecules such as proteins. 

The aim of the present paper is to use ah initio quantum mechanical methods, such as Mpller—Plesset perturbation theory b (mP2 method), to examine large clusters formed of one molecule of methanol (or water) and up to 10—12 molecules of water (or methanol). Methanol was selected because it is one of the simplest amphiphile-like molecules. Furthermore, the results will be compared to those obtained for dilute clusters of methane and water. ... 

Second-order Mpller—Plesset perturbation theory (MP2) is the quantum mechanical approach selected for the calculations because the sizes of the clusters that were employed were too large to use more accurate methods. In addition, MP2 provides accurate results regarding the calculation of the interaction energies for both H-bonded pairs and van der Waals interacting pairs. 

Solutions to the eigenvalue equation (16) can be obtained by any of the standard quantum chemical methods, such as Hartree-Fock SCF, multiconfiguration SCF (MCSCF), Mpller-Plesset perturbation, coupled cluster, or density functional theories. The matrix elements of Hr, a one-electron operator, are readily computed, thus formally the inclusion of solvent effects in the quantum mechanical description of the solute molecule appears quite simple. Moreover, gradients of the eigenvalue E are readily computed. 

AMBER = assisted model building with energy refinement force field CHARMM = chemistry at Harvard macromolecu-lar mechanics force field MP4SDQ = Mpller-Plesset fourth-order perturbation theory with corrections for single, double, and quadruple excitations OPLS = optimized potentials for liquid simulation force field TZP = triple-zeta -f polarization. 

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