![]() For linear molecules we keep tabs on 3N-5 coordinates. Using internal coordinates reduces our 3N requirement set by the Cartesian space down to a 3N-6 requirement (for non-linear molecules). With Z-matrices, we keep tabs on internal coordinates: bond length (R), bond angle (A), and torsional/dihedral angle (T/D). We increased the distance between the two atoms by some length R. What did we change? We simply changed the bond length, one variable. We now have altered the molecule in such a way that the properties of that molecule has changed. However, say we increase the distance between the hydrogen atoms. An H2 molecule centered around the origin (0,0,0) is no different from the same H2 molecule being centered around (1,1,1). The translation of the molecule through space (assuming a vacuum) will have no affect on the properties of the molecule. A point located at (0,0,1) is an absolute location for a coordinate space that extends to infinity. Cartesian space is 'absolute' so to speak. When dealing with Z-matrices, we keep track of the relative positions of points in space. The general ruling is that for Cartesian space, 3N variables must be accounted for (where N is the number of points in space you wish to index). To describe the locations of two atomic nuclei, a total of 6 variables must be written down and kept track of. Also denoted 6-31G(d).In Cartesian space, three variables (XYZ) are used to describe the position of a point in space, typically an atomic nucleus or a basis function. That a set of polarizing d-functions ( 6D) is included Maybe the most popular basis set in use today. Sets of polarization d-functions and one set of polarization f-functionsĪre added to heavy atoms, and the "2p" indicates that two sets of polarizationĪ polarized VDZ basis set from the Pople school. In addition to the 6-311G basis, the "+" indicates that diffuse s-Īnd p-functions are added to heavy atoms, the "3df" indicates that three Has been added to hydrogen also denoted 6-311G(d,p). The second asterisk indicates that a set of polarization p-functions ![]() Has been added to heavy atoms to supplement the 6-311G basis also denoted The asterisk indicates that a set of polarization d-functions ( 5D) Some workers consider this basis to be less flexible than Built like 6-31Gīut with a third layer of valence functions composed of a single, uncontracted Usually supplemented with polarization functions. (Recently-developedīasis sets don't include the "G" or its equivalent since they are essentiallyĪ popular VTZ basis set similar to the small 6-31G Stands for "Gaussian", indicating the type of primitive function. The "1" indicates that the outer valence basisįunctions are each built using a single uncontracted primitive. The "3" indicates that the inner valence basis functions are each built The "6" indicates that each core basis function is built using six primitives. Often used with a set of heavy-atom polarization functions (see 6-31G*). Includes the s-like combination (x 2 + y 2 + z 2).Ī VDZ basis set from the Pople school. Indicates that six (cartesian) functions are used in each d-set. Indicates that five functions are used in each d-set. Included to supplement the 3-21G basis, but only on second-row and heavierĪtoms (beyond neon). The asterisk indicates that a set of polarizing d-functions (6D) is ![]() Is adapted from one that was developed for a brief course within the PhysicalĪnd Chemical Properties Division at NIST ( 2). Some of the more common terminology is explainedĪn extensive list of acronyms has been published recently ( 1),Īnd a major reference work is currently in preparation. Theory and density functional theory, is cluttered with abbreviations,Īcronyms, and jargon. ![]() The literature of quantum chemistry, covering both molecular orbital Physical and Chemical Properties Division, National Institute of Standards Glossary of Common Terms and Abbreviations in Quantum Chemistry Thermochemistry: Prediction and Estimation of Molecular Thermodynamics" The following glossary is adapted from: K. ![]()
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