INTRODUCTION: AN ACCURATE INTERMOLECULAR POTENTIAL ENERGY FUNCTION FOR FLUORINE SYSTEM ALLOWS A DETAILED ANALYSIS OF THE F2 BEHAVIOR IN THE CONDENSED PHASE USING STANDARD STATISTICAL THERMODYNAMIC APPROACHES.COLLECTION OF THE CALCULATED PROPERTIES OF THE FLUORINE SYSTEM BASED ON THE OBTAINED POTENTIALS CAN BE USED TO DETERMINE THE CRITICAL PHYSICAL PROPERTIES NEEDED IN THE ACCURATE DESIGN OF THE CHEMICAL REACTIONS IN WHICH F2 IS PRODUCED OR CONSUMED. THIS FEATURE SIGNIFIES THE APPLIED IMPORTANCE OF THE COMPUTATIONAL DETERMINATION OF THE FLUORINE SYSTEM. THEREFORE, THE PURPOSE OF THE PRESENT PAPER IS TO DETERMINE ACCURATE FLUORINE PAIR-POTENTIAL ENERGY FUNCTION BY AB INITIO COMPUTATION. WE HAVE ALSO PERFORMED MD SIMULATION TO OBTAIN SOME THERMODYNAMICS AND TRANSPORT PROPERTIES OF FLUID FLUORINE AT DIFFERENT TEMPERATURES AND DENSITIES USING OUR CALCULATED TWO-BODY POTENTIAL USING THE CCSD (T) /AUG-PVDZ AB INITIO QUANTUM COMPUTATION. WE HAVE ALSO CALCULATED THE THREE-BODY INTERACTIONS FOR (F2) 3 TRIMER USING THE CCSD (T) /AUG-PVDZ AB INITIO COMPUTATIONS FOR DIFFERENT ORIENTATIONS.

BACKGROUND: EXCITATION OF THE G 2PG ELECTRON OF CS2 (X1S+G) MOLECULE INTO THE FIRST UNFILLED 3PU ORBITAL (HOMO®LUMO) GIVE RISE TO SIX VALENCE EXCITED STATS, 1,3 Å-U, 1,3DU, 1,3Å+U. IN THIS WORK WE CONSIDER ONLY OPTICALLY ALLOWED TRANSITIONS 1Å+G®1Å+U [1]. …

IN A RECENT THEORETICAL STUDY ON DE PROTONATION OF FLUOROBENZENES, THERE WAS AN EXTRAORDINARY DISCREPANCY BETWEEN THE THEORETICAL AND EXPERIMENTAL VALUES FOR ENTHALPY OF DE PROTONATION OF ORTHO- DIFLUOROBENZENESO THAT THE THEORETICAL VALUE PRESENTED 4KCAL MOL-1DEVIATION [1].THE MODERN COMPOSITE METHODS OF G4 AND G4MP2 ALONG WITH HIGH- LEVEL AB INITIO CALCULATIONS OF CCSD (T) AND QCISD (T) USING DIFFERENT BASIS SETS HAVE BEEN USED IN THIS WORK IN ORDER TO CLARIFY THE SOURCE OF DEVIATION. PREVIOUSLY, IT HAS BEEN DEMONSTRATED THAT G4MP2 PROVIDED "CHEMICAL ACCURACY" (~1.0 KCAL MOL-1) WHEREAS G4 PROVIDED EVEN BETTER RESULTS, A MEAN ABSOLUTE DEVIATION OF 0.83 KCAL MOL-1, WHEN ASSESSED AGAINST LARGE TEST SETS OF THERMOCHEMICAL DATA [2, 3]. THE RESULTS OF THE NEW COMPOSITE METHODS, G4 AND G4MP2,ALONG WITH THE HIGH LEVEL AB INITIO CALCULATIONS, CCSD (T) AND QCISD (T), ARE IN AGREEMENT WITH PREVIOUS THEORETICAL STUDIES [1]. CONSIDERING THE DEVIATIONS FOR META AND PARA ISOMERS, WHICH ARE APPROXIMATELY 2 KCAL MOL-1, A PART OF EXTRAORDINARY DEVIATION FOR ORTHO ISOMER MIGHT BE AS A RESULT OF EXPERIMENTAL VALUE. THEREFORE, FOR ORTHODIFLUOROBENZENE, WE SUGGEST A VALUE OF 380.0KCAL MOL-1, AS SHOWN BELOW, FOR WHICH THE DEVIATIONS ARE IN CONSISTENCE WITH DEVIATIONS OF OTHER ISOMERS.

WE PRESENT BENCHMARK DATABASES OF THE FIRST IONIZATION ENERGY FOR THE FIRST 18 ELEMENTS IN THE PERIODIC TABLE (H-AR). IONIZATION ENERGIES WERE CALCULATED AT 13 LEVELS OF THEORY INCLUDING TWO METHODS OF DENSITY FUNCTIONAL THEORY AND TWO METHODS OF AB-INITIO THEORY WITH 6-311++G**, AUG-CC-PVTZ AND AUG-CC-PVQZ BASIS SETS AND ONE COMPOSITE METHOD. B3LYP [1] GLOBAL HYBRIDGENERALIZED GRADIENT APPROXIMATIONS (GH-GGA) AND M06 [2] GLOBAL HYBRID-META GENERALIZED GRADIENT APPROXIMATIONS (GH-MGGA) FOR DFT THEORY, THE MP2 AND CCSD(T) METHODS OF ABINITIO CALCULATION AND GAUSSIAN-4 [3] (G4) COMPOSITE METHOD WERE USED IN PRESENT CALCULATIONS. CALCULATIONS WERE PERFORMED USING THE GAUSSIAN 09 PROGRAM. THE MULTIPLICITY OF ELEMENTS AND IONS WAS CONSIDERED AT THE STABLE STATE BASED ON PAULI EXCLUSION PRINCIPLE AND HUND'S RULE. AMONG THE TESTED METHODS, G4 GIVE THE BEST PERFORMANCE. FIG. 1. SHOWS THE CORRELATION BETWEEN THE EXPERIMENTAL DATA AND CORRESPONDING THEORETICAL DATA CALCULATED AT G4 LEVEL OF THEORY. ALSO THE RESULTS OF AB-INITIO METHODS WERE BETTER THAN DENSITY FUNCTIONAL THEORY (DFT) AND ALL OF METHODS COMBINED WITH AUG-CC-PVQZ BASIS SET SHOW A GOOD AGREEMENT WITH CORRESPONDING EXPERIMENTAL DATA AND THE BEST ONE WAS CCSD(T)/AUG-CC-PVQZ.

WE PRESENT A SYSTEMATIC INVESTIGATION, IN ORDER TO STUDY THE ACCURACY OF VARIOUS COMPUTATIONAL METHODS AND BASIS SETS THAT CAN BE APPLIED TO SURVEY THE INTERACTION OF BR-ION AND THE GASEOUS, NON POLAR CH4. BROMIDE ION INTERACTIONS WITH NEUTRAL MOLECULES, ALKANE (H-R), ARE IN THE RANGE OF WEAK INTERACTIONS SUCH AS VAN DER WAALS INTERACTIONS TO HYDROGEN BOND OR ELECTROSTATIC BOND. THE COMPUTATIONAL METHODS B3LYP, MP2 AND CCSD (T) HAVE BEEN USED FOR THE INVESTIGATION OF C-H... ANION INTERACTION IN CH4...BR-COMPLEX. IT IS NECESSARY TO EMPLOY THE LARGE ENOUGH BASIS SETS WITH DIFFUSE FUNCTIONS TO DESCRIBE ANIONIC SYSTEMS [1, 2]. WE CALCULATED THE CH4...BR- POTENTIAL ENERGY CURVE USING THE GAUSSIAN 09 FOR THREE STRUCTURES OF CH4...BR-. THESE 3 STRUCTURES ARE: CORNER-BRIDGED (1S), EDGE-BRIDGED (2S) AND FACE- BRIDGED (3S) [3]. ACCORDING TO THESE CALCULATION, THE OBTAINED POTENTIAL ENERGY CURVE SHOWED THAT, 1S STRUCTURE IS THE MOST STABLE STRUCTURE. THE RESULTS ARE REPORTED IN TABLE 1. THE POTENTIAL ENERGY WAS OBTAINED IN DIFFERENT DISTANCES OF CH4...BR-. IN ORDER TO EVALUATE ELECTRONIC ENERGIES OF ION CLUSTERS ACCURATELY, WE MADE SINGLE POINT CALCULATIONS ON OPTIMIZED GEOMETRIES TO OBTAIN POTENTIAL ENERGY CURVE FOR THE MOST STABLE STRUCTURE WITH DIFFERENT METHODS AND BASIS SET (FIGURE 1) THE BEST RESULT HAS BEEN OBTAINED BY CCSD (T) METHOD.