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--- howto:cdft [2018/11/02 12:50] – [Selected examples] nholmber
+++ howto:cdft [2018/11/02 13:11] – [Structure of input file] nholmber
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 In the above example input file, a common file ''${DFT_FILE}}'' is used as a template for the [[inp>FORCE_EVAL/DFT|DFT]] subsection. The CDFT state specific constraint settings and the wavefunction filename are passed through variables. The electronic coupling is calculated using the default weight function matrix and Löwdin orthogonalization methods. If molecular dynamics were performed with the above input file, the forces would be mixed according to linear mixing scheme $F = \lambda F_1 + (1-\lambda) F_2$, where the states $F_i$ are selected with the keyword [[inp>FORCE_EVAL/MIXED/MIXED_CDFT#FORCE_STATES|FORCE_STATES]] and the mixing parameter $\lambda$ with [[inp>FORCE_EVAL/MIXED/MIXED_CDFT#LAMBDA|LAMBDA]]. No configuration interaction calculation is performed. The [[inp>FORCE_EVAL/MIXED/MIXED_CDFT|MIXED_CDFT]] section accepts some additional keywords, which have been described in the manual.
-The keyword [[inp>FORCE_EVAL/MIXED#NGROUPS|NGROUPS]] is set to 1, which implies that the two CDFT states are treated sequentially utilizing the full set of $N$ MPI processes for the simulation. The CDFT weight function and its gradients are copied from state to state if the constraints definitions are identical in each CDFT state, because construction of these terms might be expensive in large systems. The keyword [[inp>FORCE_EVAL/MIXED#NGROUPS|NGROUPS]] could also be set to 2 in which case the CDFT weight function and gradients would first be built in parallel on $N$ MPI processes, and the two CDFT states would then calculated in parallel with $N/2$ MPI processes. This operating mode is limited to two CDFT states with one identically defined total charge density constraint. This operating mode is an advanced feature which might be useful for large scale MD simulations to save computational wallclock time at the expense of higher CPU core usage. The operating mode should only be used in conjuction with [[inp>FORCE_EVAL/MIXED/MIXED_CDFT#DLB|dynamic load balancing]] if possible, and will likely require tweaking the load balancing parameters.
+The keyword [[inp>FORCE_EVAL/MIXED#NGROUPS|NGROUPS]] is set to 1, which implies that the two CDFT states are treated sequentially utilizing the full set of $N$ MPI processes for the simulation. The CDFT weight function and its gradients are copied from state to state if the constraints definitions are identical in each CDFT state, because construction of these terms might be expensive in large systems.
+The keyword [[inp>FORCE_EVAL/MIXED#NGROUPS|NGROUPS]] could also be set to 2 or a larger value if using more than 2 CDFT states. In this case, each CDFT state is solved in parallel using $N/N_\mathrm{groups}$ processors. This will likely reduce the wall clock time of your simulation at the expense of more computing resources. However, you should note that the weight function and its gradients are computed separately for each state instead of copied from state to state (if possible). This can be costly for large solvated systems.
+A special run type is available for ''NGROUPS 2'' if the keyword [[inp>FORCE_EVAL/MIXED/MIXED_CDFT#PARALLEL_BUILD|PARALLEL_BUILD]] is activated. In this case, the CDFT weight function and gradients are first built in parallel on $N$ MPI processes, which are subsequently copied onto the two MPI processor groups of size $N/2$ which solve the CDFT states in parallel. This operating mode is limited to two CDFT states with one identically defined total charge density constraint. This operating mode is an advanced feature which might be useful for large scale MD simulations to save computational wallclock time at the expense of higher CPU core usage. The operating mode should only be used in conjuction with [[inp>FORCE_EVAL/MIXED/MIXED_CDFT#DLB|dynamic load balancing]] if possible, and will likely require tweaking the load balancing parameters.
 ==== Example: Electronic coupling of Zn cation dimer ====
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 We can use CDFT states as the basis of a configuration interaction (CI) simulation to correct for SIE in this system. As the figure above shows, CDFT-CI using the PBE functional is able to reproduce the exact dissociation profile. You can read up on the theory behind CDFT-CI simulations from the references given at the start of this tutorial. Very briefly, CDFT-CI simulations involve representing the system's wavefunction as a linear combination of multiple CDFT states where the charge/spin density is constrained differently in different states. The CI expansion coefficients and energies are then obtained by solving a generalized eigenvalue equation where the effective Hamiltonian matrix describes how the CDFT states interact with each other.
-In this tutorial, you will reproduce the DFT and CDFT results from the figure above. You can find the input files here. The reference data used to plot Figure 4 are also included in the zip-folder. Please note that the reference results were obtained with a larger basis set and planewave cutoff as well as tighter convergence criteria than the settings you will be using in this tutorial.
+In this tutorial, you will reproduce the DFT and CDFT results from the figure above. You can find the input files {{:howto:cdft-tutorial-h2.zip|here}}. The reference data used to plot Figure 4 are also included in the zip-folder. Please note that the reference results were obtained with a larger basis set and planewave cutoff as well as tighter convergence criteria than the settings you will be using in this tutorial.
   - Start by examining the simulation script ''energy.bash''. This tutorial involves a rather large number of simulations so running them will take a while. You can use the flag ''-x'' to separately run the different types of simulations (DFT, CDFT, CDFT-CI) needed in this tutorial.