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| region [2024/04/26 08:19] – [Region] werner | region [2024/07/12 08:37] (current) – external edit 127.0.0.1 |
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| Firstly, molecular orbitals are localised using the intrinsic bonding orbital (IBO) method, described in chapter [[intrinsic basis bonding analysis (IAO/IBO)]]. Occupied orbitals to be embedded are either chosen directly by the user, or the user chooses a set of atoms, and the orbitals sat on these atoms are embedded (see section [[region#selecting the Embedded Orbitals|selecting the Embedded Orbitals]]). The occupied orbitals are reordered putting the embedded orbitals at the top, followed by the other valence orbitals which are placed into the core. The embedded and active/open orbital spaces are then made pseudo-canonical. | Firstly, molecular orbitals are localised using the intrinsic bonding orbital (IBO) method, described in chapter [[intrinsic basis bonding analysis (IAO/IBO)]]. Occupied orbitals to be embedded are either chosen directly by the user, or the user chooses a set of atoms, and the orbitals sat on these atoms are embedded (see section [[region#selecting the Embedded Orbitals|selecting the Embedded Orbitals]]). The occupied orbitals are reordered putting the embedded orbitals at the top, followed by the other valence orbitals which are placed into the core. The embedded and active/open orbital spaces are then made pseudo-canonical. |
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| The virtual orbital space can also be reduced and localised to the embedding region (see section [[region#truncating the virtual space|truncating the virtual space]]). This can only be utilised by the ''FCI'' program within Molpro (and some third-party programs interfaced to Molpro), because the number of molecular orbitals no longer equals the number of basis functions. However, regional local coupled cluster can be performed [[Local correlation methods with pair natural orbitals (PNOs)|PNO-LCCSD(T)-F12 program]] (recommended, see section [[Local correlation methods with pair natural orbitals (PNOs)#correlating subsets of electrons (REGION)|correlating subsets of electrons (REGION)]]) or by the old (obsolete) DF-LCCSD programs (see section [[PAO-based local correlation treatments#correlating subsets of electrons (REGION)|correlating subsets of electrons (REGION)]] for details). | The virtual orbital space can also be reduced and localised to the embedding region (see section [[region#truncating the virtual space|truncating the virtual space]]). This can only be utilised by the ''FCI'' program within Molpro (and some third-party programs interfaced to Molpro), because the number of molecular orbitals no longer equals the number of basis functions. However, regional local coupled cluster can be performed [[Local correlation methods with pair natural orbitals (PNOs)|PNO-LCCSD(T)-F12 program]] (recommended, see section [[Local correlation methods with pair natural orbitals (PNOs)#Correlation regions in the PNO program|Correlation regions in the PNO program]]) or by the old (obsolete) [[PAO-based local correlation treatments|DF-LCCSD program]] (see section [[PAO-based local correlation treatments#correlating subsets of electrons (REGION)|correlating subsets of electrons (REGION)]] for details). |
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| ===== Defining the Orbital Spaces ===== | ===== Defining the Orbital Spaces ===== |