DMRGSCF (forte)
In this section we explain how to use block2 and forte for CASSCF and DSRG calculations with DMRG as the active space solver.
forte is an open-source package for strongly correlated methods, developed by Evangelista group.
The detailed instruction for the installation and the usage of the code can be found in
https://forte.readthedocs.io/.
Preparation
First, we need to build and install the C++ library of block2. This can be done using the -DBUILD_CLIB=ON option:
git clone -b p0.5.3rc7 https://github.com/block-hczhai/block2-preview
cd block2-preview
mkdir build
cd build
cmake .. -DUSE_MKL=ON -DBUILD_CLIB=ON -DLARGE_BOND=ON -DMPI=OFF -DCMAKE_INSTALL_PREFIX=../install
make -j 10
make install
export BLOCK2_DIR=$PWD/../install
cd ../..
After this, you will be able to find the block2 include files in ${BLOCK2_DIR}/include/ and libblock2.so in ${BLOCK2_DIR}/lib64/.
The block2Config.cmake file can be found in ${BLOCK2_DIR}/share/cmake/block2/.
Second, we need to build psi4. Make sure an eigen3 library is available in the system,
which can be installed using apt install libeigen3-dev or conda install -c omnia eigen3. If you use the conda package,
you may need to add the cmake option -DCMAKE_PREFIX_PATH=${CONDA_PREFIX} so that cmake can find it.
To save compiling time, one may install libint2 using conda install conda-forge::libint==2.8.1 before the following.
Then we can build psi4 as follows:
git clone -b v1.9 https://github.com/psi4/psi4
git pull origin master --tags
cd psi4
mkdir build
cd build
export MATH_ROOT=${CONDA_PREFIX}
cmake .. -DCMAKE_PREFIX_PATH=${CONDA_PREFIX}
make -j 10
export PSI4_DIR=$PWD/stage
cd ../..
Then we can add the following environment variables:
export PATH=${PSI4_DIR}/bin:$PATH
export PYTHONPATH=${PSI4_DIR}/lib:$PYTHONPATH
export PSI_SCRATCH=/scratch/.../psi4 # use a valid scratch folder here
Then the command psi4 should be available in the terminal. And python -c 'import psi4' should work.
If there is the error TypeError: issubclass() arg 1 must be a class, try pip install --force-reinstall typing-extensions==4.5.0.
Third, we need to build abmit as follows:
git clone -b v0.7.1 https://github.com/jturney/ambit
cd ambit
mkdir build
cd build
cmake .. -DCMAKE_INSTALL_PREFIX=../install -DENABLE_TESTS=OFF
make -j 10
make install
export AMBIT_DIR=$PWD/../install
cd ../..
Finally, we can build forte.
Here we use a revised version with the block2 interface,
which can be found in the block2_dmrg branch of the forked repo https://github.com/hczhai/forte. To build it, we can:
git clone -b block2_dmrg https://github.com/hczhai/forte
cd forte
$(psi4 --plugin-compile) -Dambit_DIR=${AMBIT_DIR}/share/cmake/ambit \
-DENABLE_block2=ON \
-Dblock2_DIR=${BLOCK2_DIR}/share/cmake/block2 \
-DCMAKE_PREFIX_PATH=${CONDA_PREFIX}
make -j 10
export FORTE_DIR=$PWD
cd ..
Then we can add the following environment variables:
export PYTHONPATH=${FORTE_DIR}:${AMBIT_DIR}/lib:$PYTHONPATH
Then python -c 'import forte' should work.
DMRG
The following is an example python script for DMRG for N2 in the minimal basis set:
import psi4
import forte
psi4.geometry("""
0 1
N 0.0 0.0 0.0
N 0.0 0.0 1.1
""")
psi4.set_options(
{
'basis': 'sto-3g',
'scf_type': 'pk',
'e_convergence': 14,
'reference': 'rhf',
'forte__active_space_solver': 'block2',
'forte__block2_sweep_davidson_tols': [1E-15],
}
)
psi4.energy('forte')
This will generate the following output:
$ grep 'Energy Summary' -A 4 dmrg.out | tail -1
1 ( 0) Ag 0 -107.654122447812 0.000000
DMRGSCF
The following is an example python script for DMRGSCF for an O2 triplet state (see DMRGSCF (pyscf) for the similar calculation using pyscf):
import psi4
import forte
psi4.geometry("""
0 3
O 0.0 0.0 -0.6035
O 0.0 0.0 0.6035
""")
psi4.set_options(
{
'basis': 'cc-pvdz',
'scf_type': 'direct',
'e_convergence': 20,
'reference': 'rohf',
'forte__job_type': 'casscf',
'forte__casscf_ci_solver': 'block2',
'forte__block2_sweep_davidson_tols': [1E-15],
'forte__restricted_docc': [2, 0, 0, 0, 0, 2, 0, 0],
'forte__active': [1, 0, 1, 1, 0, 1, 1, 1],
'forte__root_sym': 1, # B1g
}
)
psi4.energy('forte')
This will generate the following output:
$ grep 'Energy Summary' -A 4 dmrg.out | grep B1g
3 ( 0) B1g 0 -149.671533509344 2.000000
3 ( 0) B1g 0 -149.689293451723 2.000000
3 ( 0) B1g 0 -149.703603100002 2.000000
3 ( 0) B1g 0 -149.708080545113 2.000000
3 ( 0) B1g 0 -149.708521258412 2.000000
3 ( 0) B1g 0 -149.708617815460 2.000000
3 ( 0) B1g 0 -149.708645817441 2.000000
3 ( 0) B1g 0 -149.708654215054 2.000000
3 ( 0) B1g 0 -149.708656716926 2.000000
3 ( 0) B1g 0 -149.708657458784 2.000000
3 ( 0) B1g 0 -149.708657678545 2.000000
3 ( 0) B1g 0 -149.708657743713 2.000000
3 ( 0) B1g 0 -149.708657763065 2.000000
3 ( 0) B1g 0 -149.708657768818 2.000000
3 ( 0) B1g 0 -149.708657770529 2.000000
3 ( 0) B1g 0 -149.708657771038 2.000000
3 ( 0) B1g 0 -149.708657771254 2.000000
DMRG-DSRG
The following is an example python script for DMRG-DSRG for an O2 triplet state, using the DMRGSCF state as the reference state:
import psi4
import forte
psi4.geometry("""
0 3
O 0.0 0.0 -0.6035
O 0.0 0.0 0.6035
""")
psi4.set_options(
{
'basis': 'cc-pvdz',
'scf_type': 'direct',
'e_convergence': 20,
'reference': 'rohf',
'forte__job_type': 'casscf',
'forte__casscf_ci_solver': 'block2',
'forte__block2_sweep_davidson_tols': [1E-15],
'forte__restricted_docc': [2, 0, 0, 0, 0, 2, 0, 0],
'forte__active': [1, 0, 1, 1, 0, 1, 1, 1],
'forte__root_sym': 1, # B1g
}
)
e, wfn = psi4.energy('forte', return_wfn=True)
psi4.set_options(
{
'forte__job_type': 'newdriver',
'forte__active_space_solver': 'block2',
'forte__correlation_solver': 'sa-mrdsrg',
'forte__dsrg_s': 0.5,
}
)
psi4.energy('forte', ref_wfn=wfn)
This will generate the following output:
$ grep 'E0 (reference)' dsrg.out
E0 (reference) = -149.708657771253996
$ grep 'DSRG-MRPT2 correlation' -A 1 dsrg.out
DSRG-MRPT2 correlation energy = -0.263404857500777
DSRG-MRPT2 total energy = -149.972062628754770
State-Average
The following is an example python script for state-averaged DMRGSCF for three states:
import psi4
import forte
psi4.geometry("""
0 3
O 0.0 0.0 -0.6035
O 0.0 0.0 0.6035
""")
psi4.set_options(
{
'basis': 'cc-pvdz',
'scf_type': 'direct',
'e_convergence': 20,
'reference': 'rohf',
'forte__job_type': 'casscf',
'forte__casscf_ci_solver': 'block2',
'forte__block2_sweep_davidson_tols': [1E-15],
'forte__restricted_docc': [2, 0, 0, 0, 0, 2, 0, 0],
'forte__active': [1, 0, 1, 1, 0, 1, 1, 1],
'forte__avg_state': [[1, 3, 3]], # (B1g, triplet, 3 states)
}
)
psi4.energy('forte')
This will generate the following output:
$ grep '==> Energy Summary <==' -A 6 03.out | tail -3
3 ( 0) B1g 0 -149.690635774964 2.000000
3 ( 0) B1g 1 -149.093708503131 2.000000
3 ( 0) B1g 2 -148.861580599165 2.000000
Note
For realistic calculations one should not rely on the default settings for the DMRG schedule. Customized schedule can be set using for example:
'forte__block2_sweep_n_sweeps': [4, 4, 4, 6],
'forte__block2_sweep_bond_dims': [250, 500, 1000, 1000],
'forte__block2_sweep_noises': [1E-4, 1E-5, 1E-5, 0],
'forte__block2_sweep_davidson_tols': [1E-5, 1E-7, 1E-7, 1E-9],
'forte__block2_energy_convergence': 1E-8,
'forte__block2_n_total_sweeps': 18,
'forte__block2_verbose': 2