Ab initio investigation of isomerism in not rigid dimer molecules of (LiAB)2 salts with 20 valent electrons (AB-=BO-, AlO-, BS-, AlS-, CN-, CP-, SiN-, SiP-)

Ab initio calculations of potential energy surfaces in neighborhood of key structures of non rigid dimer molecules of lithium salts of (LiAB)2 type - (LiBO)2, (LiAlO)2, (LiBS)2, (LiAlS)2, (LiCN)2, (LiSiN)2, (LiCP)2, (LiSiP)2 - with 20 valent electrons are done in the framework of MP2/6-31G8//HF/6-31G* + ZPE(HF/6-31G*) and MP4SDTQ/6-31G*//MP2/6-31G* + ZPE(MP2/6-31G*) approximations. Totality of low-lying isomers containing four- and six-membered cycles with lithium bridges is localized. It is shown that for all cycles not rigidity to high deformation of angles in the case of low energy changes is characterized. Equilibrium geometrical parameters, relative energy and energy of isomer decomposition, frequency and intensities of normal vibrations are determined