Difference between revisions of "CamCASP/Programming/2"
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* '''Assembly''': All the components will be assembled into the required integrals. |
* '''Assembly''': All the components will be assembled into the required integrals. |
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| + | These modules also need to decide on what needs re-calculation when molecules rotate. If the molecular basis alters, then everything needs to be re-calculated, but if all that happens is a rotation, then some molecular quantities need not be calculated again. In particular, the density-fitting solution remains invariant with respect to rotations. But rotations mix symmetry components of a shell. For example, (px,py,pz) would be mixed into (py,pz,-px) under a rotation by 90 degrees about the z-axis. This means that, while integrals do not |
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| − | That is all straightforward. |
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| + | * |
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Revision as of 15:49, 24 February 2009
CamCASP => Programming => The DF-INTEGRAL module
Outline
This module consists of modules to calculate integrals needed for density-fitting, the density-fitting module, and modules to calculate integrals *using* primitive integrals in the auxiliary basis set and the density-fitting solution.
Through module df_int_operations and a lot of procedure overloading, a number of logical and computational operations are hidden from the higher-level energy subroutines. For example, to calculate the generalized OOOOAAAB-type 4-index Coulomb integral needed for the first-order exchange repulsion, subroutine calculate_e1exchS2 makes a call to open_gen_2eint('OOOO','AAAB',...) which does the following:
- DF: Performs the density-fitting for monomer A and dimer density-fitting. The integrals needed for the density-fitting will be automatically calculated.
- Integrals: The generalized integrals need various overlap, nuclear and 2-index Coulomb integrals. These will be identified and calculated.
- Assembly: All the components will be assembled into the required integrals.
These modules also need to decide on what needs re-calculation when molecules rotate. If the molecular basis alters, then everything needs to be re-calculated, but if all that happens is a rotation, then some molecular quantities need not be calculated again. In particular, the density-fitting solution remains invariant with respect to rotations. But rotations mix symmetry components of a shell. For example, (px,py,pz) would be mixed into (py,pz,-px) under a rotation by 90 degrees about the z-axis. This means that, while integrals do not