Double precision

Standard-state fugacities at zero pressure are evaluated using the Equation (A-2) for both condensable and noncondensable components. The Rackett Equation (B-2) is evaluated to determine the liquid molar volumes as a function of temperature. Standard-state fugacities at system temperature and pressure are given by the product of the standard-state fugacity at zero pressure and the Poynting correction shown in Equation (4-1). Double precision is advisable. 

IlyperChem uses 16 bytes (two double-precision words) of storage for each electron repulsion integral. The first 8 bytes save thecom-pressed four indices and the second S bytes store the value of the integral. Each index lakes 16 bits. Thus the maximum number of basis fiinctions is 65,535. This should satisfy all users of IlyperChem for the foreseeable future. 

Because ol Lhe use of Lwo double-precision words for each in tegral. IlyperCbem needs, for example, ahoiil 44 MByles of computer mam memory and/or disk space Lo store the elecLroii repulsion inlejrrals for benzene wilh a double-zeta 6-i lG basis set. 

JACOBIAN OB COORDINATES TRANSFORMATION Ik DERIVATIVES OF THE SHAPE FUNCTIOl lS WRT GLOBAL, VARIABT.ES IMPLICIT DOUBLE PRECISION(A-H,0-Z)... 

IMPLICIT DOUBLE PRECISION (A--H, 0-Z ) DIMENSION VEL ( >IM DF), TEMP (MAXNP) WRITE(60,6000)... 

Because of the use of two double-precision words for each integral, HyperChem needs, for example, about 44 MBytes of computer main memory and/or disk space to store the electron repulsion integrals for benzene with a double-zeta 6-3IG basis set. 

The norm is useful when doing numerical calculations. If the computer s floating-point precision is 10" , then K = 10 indicates an ill-conditioned matrix. If the floating-point precision is I0" (double precision), then a matrix with K = I0 may be ill-conditioned. Two other measures are useful and are more easily calculated ... 

Double precision—Vdilue stored as two words, rather than one, representing a real number, but allowing for approximately double the number of significant digits. 

Real—V ariable names siaiting with, A-H and O-Z, unless othetwisc declaied. Double precision-Must be declared. 

IDINT Converts a double-precision argument to Integer by truncation... 

DPROD Converts the product of two real arguments to double precision... 

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