Last Modified 27 March 2002

SCTB: Usage

Version 0.80

This is a brief description of possible uses of the sctb program, including three examples.

Computational Codes

The sctb system uses separate codes to compute different quantities. The most commonly used ones compute the total energy, atomic forces, virial, and energy second derivatives given a structure and a k-point mesh.

eval_energy.${MODEL}.${SYSTEM_TYPE} calculates the total energy of a system.
eval_forces.${MODEL}.${SYSTEM_TYPE} calculates the total energy and the forces on the atoms in the system.
eval_virial.${MODEL}.${SYSTEM_TYPE} calculates the total energy and the virial (the derivative of the energy with respect to deformation) V_ab = [ d E({ F x_i}) / d F_ab ] F^-1 where F is a deformation gradient 3x3 matrix.
eval_second_derivs.${MODEL}.${SYSTEM_TYPE} calculates the second derivatives of the energy with respect to atomic positions by computing finite-difference derivatives of the atomic forces.

Less commonly used are two testing programs that check the analytical force and virial calculations

test_forces.${MODEL}.${SYSTEM_TYPE} tests the analytical forces against finite-difference derivatives.
test_virial.${MODEL}.${SYSTEM_TYPE} tests the analytical virial against finite-difference derivatives.

Examples

To show the usage of the program, we have provided several examples. They show the construction of the input files and how to obtain the auxillary files needed to run the code, as well has how to interpret the output files.

Example 1 shows how to run the serial code in interactive mode. The example calculates the total energy and forces on a 1x1 unit cell of a silicon surface using k-point summation with the serial code.
Example 2 shows a slightly different example of serial runs in interactive mode, calculating the total energy and forces on a vacancy in a silicon bulk system using the gamma point only with the serial code.
Example 3 shows how to run the serial and parallel codes in batch mode on the IBM SMP at ASC. The runs calculate the total energy and virial on a 1x1 unit cell of a silicon surface using k-point summation, comparing non-charge-self-consistent and charge-self-consistent modes. This is the Alpha test problem.

While every effort has been made to insure that these scripts will run on most Unix/Linux machines with the appropriate software installed, installations to differ and a particular script may not work on your system. In other words, your mileage may vary.

Other examples will be developed as time permits.

sctb Home Page Introduction About Version 0.80 Installation List of Files Usage Input Files Output Files Trouble Shooting Appendix