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qmcchem/README.md

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QMC=Chem : Quantum Monte Carlo for Chemistry
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============================================
QMC=Chem is the quantum Monte Carlo program of the
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[Toulouse (France) group](http://qmcchem.ups-tlse.fr).
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It is meant to be used in the *post-Full-CI* context : a quasi-Full-CI
calculation is done with the
[quantum package](https://github.com/LCPQ/quantum_package),
and this wave function is used as a trial wave function for the fixed-node
diffusion Monte Carlo algorithm.
* Parallel efficiency of 98.3% on 16_000 cores
* The load balancing is optimal: the workers always work 100% of the time,
independently of their respective CPU speeds
* Efficient: 0.96 Pflops/s on 76_800 cores of Curie in 2011
* All network communications are non-blocking,
with the [ZeroMQ](http://zeromq.org) library
* All the implemented algorithms are CPU-bound : the only limit
is the available CPU time
* The number of simultaneous worker nodes can be variable during a calculation
* Fully fault-tolerant (crashing nodes don't stop the running calculation)
* QMC=Chem has been used in grid environments (EGI european grid) and
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in Cloud environments (France Grilles) coupled to supercomputers
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Warnings:
* QMC=Chem is under the GPLv2 license. Any modifications to or
software including (via compiler) GPL-licensed code must also be made available
under the GPL along with build & install instructions.
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Requirements
------------
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* [OCaml compiler with Opam and Core library](http://github.com/ocaml)
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* [ZeroMQ high performance communication library](http://www.zeromq.org)
* [F77_ZMQ ZeroMQ Fortran interface](http://github.com/scemama/f77_zmq/)
* [IRPF90 Fortran code generator](http://irpf90.ups-tlse.fr)
* [EZFIO Easy Fortran I/O library generator](http://github.com/scemama/EZFIO)
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* GNU C++ Compiler (g++) for ZeroMQ
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* Python >= 2.6 for install scripts
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* Bash for install scripts
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* Fortran compiler, Intel Fortran recommended
* Lapack library, Intel MKL recommended
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Most of the dependencies are open-source can be downloaded automatically by
going into the `install` directory and running `make`. It will first download
into the `install/Downloads` directory everything that needs to be installed.
The building of the dependencies takes place in the `install/_build`
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directory, and the packages that are being installed can be followed by looking
at the log files in this directory. When a package was successfully installed,
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a `*.ok` file is created and the log file is deleted.
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If you don't have an internet connection available, you can execute the
downloading step on another computer and transfer all the downloaded files
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into the `Downloads` directory.
The Fortran and C++ compilers, Python and Bash interpreters and the Lapack
library need to be installed manually by the user.
Installation
------------
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The `make.config` file contains compiler specific parameters. You should change
them to match your hardware. You can copy the `make.config.ifort` or
`make.config.gfortran` as a starting point.
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Before using or compiling QMC=Chem, environment variables need to be loaded. The
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environment variables are located in the `qmcchemrc` file:
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```bash
$ source qmcchemrc
```
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The `QMCCHEM_NIC` environment variable should be set to the proper network interface,
usually `ib0` on HPC machines.
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To compile the program, run
```bash
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$ make
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```
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Example of a QMC=Chem calculation
---------------------------------
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1.Calculation with the [quantum package](http://github.com/QuantumPackage/qp2)
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Create the `xyz` file containing the nuclear coordinates of the system
```bash
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$ cat > h2o.xyz << EOF
3
Water molecule
O 0. 0. 0.
H 0.9572 0. 0.
H -0.239987 0.926627 0.
EOF
```
Choose a suitable basis set and create the [EZFIO database](https://github.com/LCPQ/ezfio)
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```bash
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$ qp_create_ezfio -b cc-pvdz h2o.xyz -o h2o
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```
Run the SCF calculation
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```bash
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$ qp_run scf h2o
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```
Run the CIPSI calculation
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```bash
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$ qp_run fci h2o
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```
Transform the input for use in QMC=Chem
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```bash
$ qp_run save_for_qmcchem h2o
```
2.FN-DMC calculation with QMC=Chem
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Before using QMC=Chem, you need to load the environment variables:
```bash
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$ source qmcchemrc
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```
In QMC=Chem, everything goes through the use of the ``qmcchem`` command.
When a command is run with no arguments, it prints a help message.
This is mainly the manual of QMC=Chem. For example:
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```
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$ qmcchem
QMC=Chem command
qmcchem SUBCOMMAND
=== subcommands ===
debug Debug ZeroMQ communications
edit Edit input data
md5 Manipulate input MD5 keys
result Displays the results computed in an EZFIO directory.
run Run a calculation
stop Stop a running calculation
version print version information
help explain a given subcommand (perhaps recursively)
missing subcommand for command qmcchem
$ qmcchem edit
Run a calculation
qmcchem run EZFIO_FILE
Run QMC=Chem
=== flags ===
[-a] Add more resources to a running calculation.
[-d] Start a dataserver process on the local host.
[-q <dataserver_addr>] Start a qmc process on the local host.
[-s <host>] Start a qmc process on <host>.
[-help] print this help text and exit
(alias: -?)
missing anonymous argument: EZFIO_FILE
```
1) Set the parameters for a VMC calculation to create initial walker positions
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```
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$ qmcchem edit -h
Edit input data
qmcchem edit EZFIO_FILE [INPUT]
Edit input data
=== flags ===
[-c] Clear blocks
[-e energy] Fixed reference energy to normalize DMC weights
[-f 0|1] Correct wave function to verify electron-nucleus cusp
condition
[-j jastrow_type] Type of Jastrow factor [ None | Core | Simple ]
[-l seconds] Length (seconds) of a block
[-m method] QMC Method : [ VMC | DMC ]
[-n norm] Truncation t of the wave function : Remove determinants
with a
contribution to the norm less than t
[-s sampling] Sampling algorithm : [ Langevin | Brownian ]
[-t seconds] Requested simulation time (seconds)
[-ts time_step] Simulation time step
[-w walk_num] Number of walkers per CPU core
[-wt walk_num_tot] Total number of stored walkers for restart
[-help] print this help text and exit
(alias: -?)
$ qmcchem edit h2o -f 1 -m VMC -n 1.e-5 -s Langevin -t 300 -l 10
```
3) Get info on the wave function
```bash
$ qmcchem info h2o
```
4) Run the VMC calculation
```bash
$ qmcchem run h2o
```
5) Set the correct parameters for FN-DMC
```bash
$ qmcchem edit h2o -e -76.438 -m DMC -s Brownian -ts 3.e-4 -t 3600 -l 30
```
6) Run the FN-DMC calculation
```bash
$ qmcchem run h2o
```
7) Print the result
```bash
$ qmcchem result h2o
```
References
----------
[Quantum Monte Carlo for large chemical systems: Implementing efficient strategies for petascale platforms and beyond](http://dx.doi.org/10.1002/jcc.23216)
> Anthony Scemama , Michel Caffarel , Emmanuel Oseret and William Jalby (2013), in: Journal of Computational Chemistry, 34:11(938--951)
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[Quantum Monte Carlo with very large multideterminant wavefunctions](http://arxiv.org/abs/1510.00730)
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> Anthony Scemama , Thomas Applencourt , Emmanuel Giner and Michel Caffarel (2015), in: ArXiv ePrints:arXiv:1510.00730v2 [physics.chem-ph]
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