Quick Start Tutorial

This tutorial walks you through your first MAPLE calculations. By the end, you will know how to run a single-point energy calculation, perform a geometry optimization, and read the output files.

Your First Calculation

Let's start with the simplest task: computing the single-point energy of a water molecule. Create a file named water_sp.inp with the following content:

#model = ani2x
#device = cpu

O    0.000000    0.000000    0.117300
H    0.000000    0.757200   -0.469200
H    0.000000   -0.757200   -0.469200

Run the calculation with:

maple water_sp.inp

Since no task type is specified, MAPLE defaults to a single-point energy calculation. The output will display the electronic energy in Hartree units:

Energy: -76.389412305821

Geometry Optimization

To optimize the geometry of a molecule, add the #opt command. Create a file named water_opt.inp:

#model = ani2x
#device = cpu
#opt

O    0.000000    0.000000    0.120000
H    0.000000    0.800000   -0.480000
H    0.000000   -0.800000   -0.480000

Run it:

maple water_opt.inp

MAPLE will iteratively adjust the atomic positions to minimize the energy. The output shows the progress of each optimization step:

Iteration   E(Eh)            dE(kcal/mol)   max(|G|)    RMS(G)
Convergence thresholds                      0.000450    0.000300
  0        -76.389012          0.00         0.012345    0.005678
  1        -76.389398         -0.24         0.003210    0.001234
  2        -76.389412         -0.01         0.000321    0.000142

Optimization converged in 2 steps.

You can customize the optimization method and convergence criteria. For example, to use the L-BFGS optimizer with a tighter convergence threshold:

#model = ani2x
#opt(method=lbfgs, convergence=1e-6)

O    0.000000    0.000000    0.120000
H    0.000000    0.800000   -0.480000
H    0.000000   -0.800000   -0.480000

Reading Output

MAPLE writes results to the terminal and to output files. The primary output includes:

• Energy: The electronic energy in Hartree (Eh) at each step.
• dE: The energy change from the previous step in kcal/mol.
• max(|G|): The maximum component of the gradient (atomic forces).
• RMS(G): The root-mean-square of the gradient.

Convergence is reached when both max(|G|) and RMS(G) fall below their respective thresholds, as shown in the convergence threshold line of the output.

For optimization jobs, the optimized geometry is written to an XYZ file that you can visualize with molecular viewers such as ASE GUI, Avogadro, or VMD:

# View the optimized structure with ASE
ase gui water_opt.xyz

Next Steps

Now that you have run your first MAPLE calculations, explore these topics to learn more: