ADAMAS program is designed to perform fast calculations of energies and mechanical properties of carbon allotropes. It is based on deductive molecular mechanics approach, allowing to derive a force field from geminal (valence bond) theory.
- Note
- Present version of ADAMAS supports carbon allotropes with four-coordinated atoms only. The part of the code, dealing with delocalized \pi-systems, is still on progress.
Description of input files.
To run the program User needs to provide two input files called 'dmmin' and 'POSCAR'. Second one is just a standard POSCAR file, describing the crystal structure of allotrope. You can find format description in the VASP Wiki page. File 'dmmin' contains several settings, which needs to be specified by User. Each setting has its own fixed keyword and may have several possible values. There are default values of each setting in the program, so User can just use them. Here are the brief description of input variables:
- Parameterization scheme (a way to parametrize semi-empirical Hamiltonian) which is going to be used. Keyword used for this setting is 'PARAMETERIZATION:' (all keywords may be written by lowercase also). Present version of the program supports two schemes: CNDO and MNDO, thus possible values of present setting are 'CNDO' and 'MNDO' respectively.
- Approximation used to evaluate SLG reduced density matrices (RDMs). Corresponding keyword is 'SLG_DENSITY:'. This setting has two possible values: 'mean' and 'corr'. First one corresponds to mean field approximation and second one takes correlation corrections into account.
- The basis set which is going to be used. Key word: 'BASIS_SET:'. Present version of the program supports three types of basis sets: i) basis of single Slater type orbitals; ii) two parametric hydrogen-like basis set (H-2 set); iii) three parametric hydrogen-like basis set (H-3 set). Respective values of this setting are 'STO', 'H-2' and 'H-3'.
- Orbital exponents have default values for each basis set (for STO they are exponents corresponding to parameterization scheme used, for H-2 and H-3 sets they are values obtained by minimizing energy of free atom). However, values of orbital exponents may be varied by User. To do this key word 'ORBITAL_EXPONENTS:' may be used. If default values of orbital exponents are plaining to be used, then this setting should have value 'Default'. Otherwise User should specify orbital exponents after this key word. It should be noted that STO basis requires one exponent, H-2 requires two exponents and H-3 requires three exponents. For H-2 basis exponents should be written in the order: 2s, 2p. For H-3 basis in the order: 1s, 2s, 2p.
- Resonance parameters of carbon may either have standard values (depending on parameterization) or may be specified by user. To enter resonance parameters keyword 'RESONANCE_PARAMETERS:' is used. If values of resonance parameters are going to be standard, then 'Default' value should be assigned to this keyword. Otherwise User should specify resonance parameters in the following order: ss, sp, pp, PiPi.
- A number of layers used to evaluate nonbond interactions. Key word: 'NUMBER_OF_LAYERS: '. This parameter shows, how many layers of unit cells are going to be taken into account in nonbond energy calculations. Its value corresponds to the maximum number of translations on each unit vector. Default value of this setting is 7.
Example of 'dmmin' file:
PARAMETERIZATION: MNDO
SLG_DENSITY: mean
BASIS_SET: STO
ORBITAL_EXPONENTS: 1.787537
RESONANCE_PARAMETERS: 0.62964 0.48650 0.34336 0.37875
NUMBER_OF_LAYERS: 4
Example of POSCAR file for diamond:
Diamond
1.00000
1.7827 1.7827 0.0000
0.0000 1.7827 1.7827
1.7827 0.0000 1.7827
C
2
Direct
0.0 0.0 0.0
0.25 0.25 0.25
1.9.2