/usr/include/chemps2/FourIndex.h is in libchemps2-dev 1.8.3-2.
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CheMPS2: a spin-adapted implementation of DMRG for ab initio quantum chemistry
Copyright (C) 2013-2016 Sebastian Wouters
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#ifndef FOURINDEX_CHEMPS2_H
#define FOURINDEX_CHEMPS2_H
#include "Irreps.h"
namespace CheMPS2{
/** FourIndex class.
\author Sebastian Wouters <sebastianwouters@gmail.com>
\date February 8, 2013
Container class for four-index tensors with Abelian point group symmetry (real character table; see Irreps.h): 2-particle matrix elements. The four-index tensor element V_ijkl has 8-fold permutation symmetry and is only nonzero when I_i x I_j = I_k x I_l. To clarify the convention, the potential energy is given: \n
\f$\frac{1}{2} \sum\limits_{ijkl\sigma\tau} V_{ijkl} \delta_{I_i \otimes I_j \otimes I_k \otimes I_l, I_{trivial}} \hat{a}_{i \sigma}^{\dagger} \hat{a}_{j \tau}^{\dagger} \hat{a}_{l \tau} \hat{a}_{k \sigma} \f$.\n
Hence \f$ V_{ijkl} = ( ij \mid V \mid kl ) \f$ in physics notation, i.e. with i and k the same integration coordinate for the electron repulsion integrals.
*/
class FourIndex{
public:
//! Constructor
/** \param nGroup The symmetry group number (see Irreps.h)
\param IrrepSizes Array with length the number of irreps of the specified group, containing the number of orbitals of that irrep */
FourIndex(const int nGroup, const int * IrrepSizes);
//! Destructor
virtual ~FourIndex();
//! Set all two-body matrix elements to zero
void Clear();
//! Set an element
/** \param irrep_i The irrep number of the first orbital (see Irreps.h)
\param irrep_j The irrep number of the second orbital
\param irrep_k The irrep number of the third orbital
\param irrep_l The irrep number of the fourth orbital
\param i The first index (within the symmetry block)
\param j The second index (within the symmetry block)
\param k The third index (within the symmetry block)
\param l The fourth index (within the symmetry block)
\param val The value to which the element of the matrix should be set */
void set(const int irrep_i, const int irrep_j, const int irrep_k, const int irrep_l, const int i, const int j, const int k, const int l, const double val);
//! Add a double to an element
/** \param irrep_i The irrep number of the first orbital (see Irreps.h)
\param irrep_j The irrep number of the second orbital
\param irrep_k The irrep number of the third orbital
\param irrep_l The irrep number of the fourth orbital
\param i The first index (within the symmetry block)
\param j The second index (within the symmetry block)
\param k The third index (within the symmetry block)
\param l The fourth index (within the symmetry block)
\param val The value which should be added to the matrixelement */
void add(const int irrep_i, const int irrep_j, const int irrep_k, const int irrep_l, const int i, const int j, const int k, const int l, const double val);
//! Get an element
/** \param irrep_i The irrep number of the first orbital (see Irreps.h)
\param irrep_j The irrep number of the second orbital
\param irrep_k The irrep number of the third orbital
\param irrep_l The irrep number of the fourth orbital
\param i The first index (within the symmetry block)
\param j The second index (within the symmetry block)
\param k The third index (within the symmetry block)
\param l The fourth index (within the symmetry block) */
double get(const int irrep_i, const int irrep_j, const int irrep_k, const int irrep_l, const int i, const int j, const int k, const int l) const;
//! Get a given irrep size
/** \param irrep The irrep for which you want to know the irrep size
\return The corresponding irrep size */
int get_irrep_size( const int irrep ) const;
//! Save the FourIndex object
/** \param name filename */
void save(const std::string name) const;
//! Load the FourIndex object
/** \param name filename */
void read(const std::string name);
#ifdef CHEMPS2_MPI_COMPILATION
//! Broadcast the ERI to all processes
/** \param ROOT The process which should broadcast */
void broadcast( const int ROOT );
#endif
private:
//Contains the group number, the number of irreps, and the multiplication table
Irreps SymmInfo;
//Array with length the number of irreps of the specified group, containing the number of orbitals of that irrep
int * Isizes;
/*The following conventions are used for storage:
- 8-fold permutation symmetry: V_ijkl = V_jilk = V_ilkj = V_lijk = V_kjil = V_jkli = V_klij = V_lkji
- Reorder indices until V_ijkl (I_i x I_j = I_k x I_l --> stored per center symm block):
- I_i <= I_j <= I_l and I_i <= I_k
- Icenter == Itriv : I_i == I_j and I_k == I_l
- Icenter > Itriv : I_i < I_j and I_k != I_l
- Vmat[Icenter][I_i][I_k] --> only created if ordering of all sectors is ok (I_i <= Icent x I_i ; I_k >= I_i ; Icent x I_k >= I_cent x I_i)
- Once the order is established based on symmetry sectors, the order within symmetry sectors has to be set too:
- Case Icenter == Itrivial :
- If I_i == I_j == I_k == I_l : index (within symm block) i smallest; l>=j>=i and k>=i ; if i==j then l>=k
- Vmat[Itriv][I_i][I_i][i + k(k+1)/2]
- if i==j --> [j-i][l-k]
- if i< j --> [j-i][l-j]
- If I_i == I_j < I_k == I_l : index i<=j ; if i<j then k and l fixed ; if i==j then l>=k
- Vmat[Itriv][I_i][I_k][i + nOrbWithIrrepI_i * k]
- if i==j --> [j-i][l-k]
- if i< j --> [j-i][l]
- Case Icenter > Itrivial (I_i < I_j and I_k != I_l) :
- If I_i == I_k and hence I_j == I_l : index k>=i and index l>=j
- Vmat[Icent][I_i][I_i][i + k*(k+1)/2][j][l-j]
- If I_i < I_k and hence I_j < I_l : fixed by block order
- Vmat[Icent][I_i][I_k][i + nOrbWithIrrepI_i * k][j][l] */
long long ***** storage;
//Calculate the number of unique FourIndex elements --> true means allocate the storage and false means deallocate the storage!
long long calcNumberOfUniqueElements(const bool allocateStorage);
//The number of unique FourIndex elements
long long arrayLength;
//The actual two-body matrix elements
double * theElements;
//Functions to get the correct pointer to memory
long long getPointer(const int irrep_i, const int irrep_j, const int irrep_k, const int irrep_l, const int i, const int j, const int k, const int l) const;
long long getPtrIrrepOrderOK(const int irrep_i, const int irrep_j, const int irrep_k, const int irrep_l, const int i, const int j, const int k, const int l) const;
long long getPtrAllOK1(const int Icent, const int irrep_i, const int irrep_k, const int i, const int j, const int k, const int l) const;
long long getPtrAllOK2(const int Icent, const int irrep_i, const int irrep_k, const int i, const int j, const int k, const int l) const;
long long getPtrAllOK5(const int Icent, const int irrep_i, const int irrep_k, const int i, const int j, const int k, const int l) const;
};
}
#endif
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