In OpenERP first, install the account module and then create the own module and relate it to the fields payment term in account module.

Follow these steps given below:

Step1- First create add_penalty.py file in your own module and pass this file in your __init__.py file. Then create a function and pass this function in button.

Use this code given below:

import time
from lxml import etree
import decimal_precision as dp
from tools.translate import _
import netsvc
import pooler
from osv import fields, osv, orm
import datetime
from datetime import datetime
from datetime import date, timedelta
import types
class add_penalty(osv.osv):
    _name = 'add.penalty'
    def _get_result(self,cr,uid,ids,name,args,context=None):
        res={}
        invoice = self.pool.get('account.invoice')
        cr.execute("select sum(amount_total) from account_invoice")
        invoices = cr.fetchone()
        if invoices:
            name = invoices[0]
            for inv in self.pool.get('add.penalty').browse(cr, uid, ids, context=context):
                res[inv.id] = name
        return res    
    _columns ={
                'date':fields.date('Date'),
                'test':fields.function(_get_result,'Grand Total', store = True),
            }
    def get_result(self,cr,uid,ids,context=None):     
        invoice = self.pool.get('account.invoice')
        cr.execute("select sum(amount_total) from account_invoice")
        invoices = cr.fetchone()
        if invoices:
            name = invoices[0]            
        raise orm.except_orm(_('Sum'), str(name))
        return True
    def test_amount(self, cr, uid, ids,context=None):   
        res = {}
        date_diff = 0
        now = datetime.now()        
        now = now.strftime('%Y-%m-%d')
        date_now = datetime.strptime(now,'%Y-%m-%d')
        dt = date_now
        name = 'CD Break'
        comment = 'Write-Off'
        cd_flag = True
        tname = 'None'
        qty = 1
        rate = 1.00
        amount = 0.0
        amt = 0.0
        pay_option = 'without_writeoff'
        mline_state = 'valid'
        move_state = 'draft'
        ptype = 'dr'
        v_state = 'draft'
        v_type = 'sale'         
        seq_id = self.pool.get('ir.sequence').search(cr, uid, [('name','=','Sales Journal')])[0]
        vnumber = self.pool.get('ir.sequence').next_by_id(cr, uid, seq_id)
        ref = vnumber.replace('/','')
        account = self.pool.get('account.account')
        acc_id = 11
        acc_id1 = 39
        j_id = 1
        invoice = self.pool.get('account.invoice')        
        cr.execute("select * from account_invoice where state = 'open' and payment_term > 0 and cash_credit='Credit Tax Invoice'")
        invoices = invoice.browse(cr, uid, map(lambda x: x[0], cr.fetchall()) )
        for inv in invoices:            
            if (inv.penalty_date):
                dt = datetime.strptime(inv.penalty_date,'%Y-%m-%d')
            elif inv.date_due:
                dt = datetime.strptime(inv.date_due,'%Y-%m-%d')
            date_diff = date_now - dt
            if inv.state == 'open' and date_diff.days >=30:
                amount = inv.residual * 0.03
                inv.residual += amount
                inv.amount_total += amount
                orig = inv.origin              
                if orig:
                    line = self.pool.get('account.move.line')
                    cr.execute("SELECT id FROM account_move_line WHERE ref = %s",(orig,))
                    lines = line.browse(cr, uid, map(lambda x: x[0], cr.fetchall()) )
                    product = self.pool.get('product.product')                    
                    credit_flag = 'true'                    
                    serial = str(name + '-' + inv.serial_number)
                    for l in lines:                        
                        if l.debit > 0.00:                            
                            l.debit += amount                            
                        if l.credit > 0.00 and l.product_id.id > 0 and credit_flag == 'true':
                            credit_flag = 'false'                                               
                            l.credit += amount
                            cr.execute('insert into account_invoice_line (origin,account_id,name,invoice_id,price_unit,quantity,partner_id,price_subtotal,tax_name) values (%s, %s, %s, %s, %s, %s, %s, %s, %s)', (orig,inv.account_id.id,name,inv.id,amount,qty,inv.partner_id.id,amount,tname)) 
                            cr.execute('insert into account_voucher (create_date,date,type,partner_id,comment,company_id,account_id,period_id,move_id,journal_id,amount,payment_rate_currency_id,payment_rate,payment_option,state,number) values (%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s) RETURNING id', (datetime.now(),datetime.now(),v_type,inv.partner_id.id,comment,inv.company_id.id,acc_id,inv.period_id.id,inv.move_id.id,inv.journal_id.id,amount,inv.currency_id.id,rate,pay_option,v_state,vnumber,))
                            v_id = cr.fetchone()
                            cr.execute('insert into account_voucher_line (create_date,voucher_id,company_id,account_id,name,amount,type) values (%s,%s,%s,%s,%s,%s,%s)',(datetime.now(),v_id,inv.company_id.id,acc_id1,name,amount,ptype))
                            cr.execute('insert into account_move (name,journal_id,period_id,partner_id,date,state,ref) values(%s,%s,%s,%s,%s,%s,%s) RETURNING id' ,(vnumber,j_id,inv.period_id.id,inv.partner_id.id,datetime.now(),move_state,ref))
                            move = cr.fetchone()
                            cr.execute('insert into account_move_line (create_date,journal_id,partner_id,credit,debit,ref,account_id,period_id,company_id,date,move_id,name,state) values (%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s)',(datetime.now(),j_id,inv.partner_id.id,amt,amount,ref,acc_id,inv.period_id.id,qty,datetime.now(),move,serial,mline_state))
                            cr.execute('insert into account_move_line (create_date,journal_id,partner_id,credit,debit,ref,account_id,period_id,company_id,date,move_id,name,state) values (%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s,%s)',(datetime.now(),j_id,inv.partner_id.id,amount,amt,ref,acc_id1,inv.period_id.id,qty,datetime.now(),move,name,mline_state))
                    cr.execute("update account_invoice set penalty_date=%s, cd_break=%s where id=%s",(datetime.now(),cd_flag,inv.id,))
        return True

    def button_compute(self, cr, uid, ids, context=None, set_total=False):
        for line in self.browse(cr, uid, ids, context=context):
            if set_total:
                self.pool.get('add.penalty').write(cr, uid, [line.id], {'name': line.name})
        return True

add_penalty()

Step2- Then create add_penalty.xml file in your own module and pass this file in __openerp__.py file.

Use this code given below:

<?xml version="1.0" ?>
<openerp>
    <data>       
        <record id="view_invoice_penalty_form" model="ir.ui.view">
            <field name="name">penalty.form</field>
            <field name="model">add.penalty</field>
            <field name="type">form</field>
            <field name="arch" type="xml">
                <form string="Penalty" >
					<field name="date"/>
                    <button name="test_amount" string="Penalty" icon="gtk-execute" type="object"/>			
                </form>
            </field>
        </record>
         
         <record id="ir_cron_mail_gateway_action" model="ir.cron">
            <field name="name">Auto Penalty</field>
            <field name="interval_number">1</field>
            <field name="interval_type">days</field>
            <field name="numbercall">-1</field>
            <field name="doall" eval="False"/>
            <field name="model">add.penalty</field>
            <field name="function">test_amount</field>
           <field eval="'()'" name="args"/>
        </record>           	
		<record model="ir.actions.act_window" id="action_penalty_form">
			<field name="name">Add penalty</field>
			<field name="res_model">add.penalty</field>
		</record>		
		<menuitem name="Add Penalty" id="menu_penalty" parent="account.menu_finance" action="action_penalty_form" sequence="2"/>		
	</data>
</openerp>