NN3DHO - Neural Network 3D Harmonic Oscillator

   NN3DHO is a Fortran code to solve the quantum 3D harmonic oscillator using 
   neural networks as trial wave function and variational quantum Monte Carlo.

   The Trial neural network wavefunction is written as:
     \Psi ( \vec r ) = \Phi_{NN} ( \vec R ) / ( alpha**2 + r**2 )**2 

      where \Phi_{NN} is the neural network output.

   The neural network implentation is a modified version of:

       @article{10.1145/3323057.3323059,
         author = {Curcic, Milan},
         title = {A Parallel Fortran Framework for Neural Networks and Deep Learning},
         year = {2019},
         issue_date = {December 2018},
         publisher = {Association for Computing Machinery},
         address = {New York, NY, USA},
         volume = {38},
         number = {1},
         issn = {1061-7264},
         url = {https://doi.org/10.1145/3323057.3323059},
         doi = {10.1145/3323057.3323059},
       }

     The random number generator used is from SPRNG library. 
     More details in http://www.sprng.org/

   Requirements
     - SPRNG, The Scalable Parallel Random Number Generators Library

   Compiling the code:
     ---
     Set the correct path to the SPRNG library using the variable SPRDIR in
     the makefile.
     ---
     make

   Running the code:

     Consider PATH_NN3DHO to be the path to the main folder of the program.
     After compiling successfully, there will a folder called "bin" on the
     PATH_NN3DHO. Inside "bin", there will be the executable 'nn3dho.run'.

     To run the code, you just need to execute nn3dho.run
      >> PATH_NN3DHO/bin/nn3dho.run
     If you are inside the folder examples, for instance, you can run the command: 
      >> ../bin/nn3dho.run
 
     The program reads the file '3dhonn.in' inside the folder where the program was 
     run. This file must have the same structure as the file inside the folder 
     examples. If there is not a file called '3dhonn.in' on the folder, default 
     parameters will be used.