apbs-coulomb: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/apbs-coulomb - from package: apbs-tools

You may install the required package with command yum install {package}

Error in other languages:
apbs-coulomb: bevel nie gevind nie
apbs-coulomb: comandă negăsită
apbs-coulomb: comando não encontrado
apbs-coulomb: commande introuvable
apbs-coulomb: command not found
apbs-coulomb: käsku ei ole
apbs-coulomb: không tìm thấy lệnh
apbs-coulomb: komanda nerasta
apbs-coulomb: Kommando nicht gefunden.
apbs-coulomb: kommandot finns inte
apbs-coulomb: komut yok
apbs-coulomb: nie znaleziono polecenia
apbs-coulomb: níor aimsíodh an t-ordú
apbs-coulomb: no se encontró la orden
apbs-coulomb: no s'ha trobat l'ordre
apbs-coulomb: opdracht niet gevonden
apbs-coulomb: parancs nem található
apbs-coulomb: perintah tidak ditemukan
apbs-coulomb: príkaz nenájdený
apbs-coulomb: příkaz nenalezen
apbs-coulomb: команда не найдена
apbs-coulomb: командата не е открита
apbs-coulomb: 命令找不到
apbs-coulomb: コマンドが見つかりません